Is the interior of a Bag of Holding actually an extradimensional space?

Question

In D&D 5e, is the inside of a bag of holding actually described anywhere as being an extradimensional space/demiplane?

The description of the bag of holding doesn't actually explicitly state that it is, it only implies it with its mentioning of "This bag has an interior space considerably larger than its outside dimensions", and talking about scattering contents into the Astral Plane and what happens when you combine it with certain other magic items...

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Speaking of which, the handy haversack says:

This backpack has a central pouch and two side pouches, each of which is an extradimensional space.

and the portable hole says:

You can use an action to unfold a portable hole and place it on or against a solid surface, whereupon the portable hole creates an extradimensional hole 10 feet deep.
[...]
The cylindrical space within the hole exists on a different plane, so it can't be used to create open passages.
[...]
Folding the cloth closes the hole, and any creatures or objects within remain in the extradimensional space.

In other words, these other two items explicitly state that they create extradimensional spaces, and the portable hole even goes as far as stating that the space is another plane. The bag of holding description says no such thing, leaving us to simply infer that it probably is an extradimensional space.

Am I missing something? Is there something more conclusive rather than my above inference that the inside of a bag of holding is actually an extradimensional space?

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I ask because this came up in our last session; a player and the DM discussed it, the player arguing that it was, and the DM pointed out that the DMG didn't actually say it was, although the DM eventually decided to go with it (especially since a couple other players, myself included, piped up with that we had always been under the impression that it was).

The player arguing that it was has played previous editions of D&D, so maybe it was explicitly stated there, which I would be interested to know, but I'm primarily after any 5e evidence that it is besides the inference included in the question.

Answer 1

Yes, Bags of Holding create extradimensional space

From the description of Portable Hole:

[snip]...Placing a portable hole inside an extradimensional space created by a bag of holding, Heward's handy haversack, or similar item ...[snip]

(similar wording exists for the Bag of Holding and Heward's Handy Haversack, as well)

Answer 2

Yes it does, as @goodguy5 shows. Since you showed an interest in this ...

Edition comparison: "extra dimensional" space is alluded to sometimes

The original item from OD&D

Bag of Holding: A sack-sized magical bag which will contain 10,000 Gold Pieces as if they were only 300. Objects up to 10' length and 5' width and 3' height may be stuffed into the bag, but the weight equivalent, regardless of the weight of the object, then becomes 600. (Monsters and Treasures, TSR, 1974, p. 36)

As with most OD&D, less detail than the next edition, which referred to dimensional something

AD&D 1e.

What the distinction is between 'extra dimensional' and 'non dimensional' is unclear to me, although it may be Gygax using words with some what less precision than later writers and devs use.

Bag of Holding: As with other magic bags, this one appears to be a common cloth sack of about 2' X 4' size. The bag of holding opens into a non-dimensional space, and its inside is larger than its outside dimensions. Regardless of what is put into this item, the bag of holding always weighs a fixed amount. This weight, the bag's weight limit in contents, (DMG, AD&D 1e, p. 138)

BECMI

Basic has a description of it, none of E/C/M/I do. (Thanks to @JohnP)

Bag of Holding: This item looks like a normal small sack, but anything placed within it disappears. Anyone may reach in and find the contents by touch. The bag will actually hold treasures up to 10,000 en in weight, but will only weigh 600 en when full. An item to be placed inside the bag may be no larger than 10' x 5' x 3'. A larger item will not fit inside.

This edition had a "max cube" delineation that isn't in the current edition. As with OD&D, no term with "non dimensional" or "extra dimensional" as a descriptive was used.

AD&D 2e

Same as AD&D 1e.

D&D 3.5

The initial description is nearly identical to the AD&D 1e, in that it refers to non dimensional space, rather than extra dimensional space, but there is more detailed treatment of what happens to it after the table is consulted regarding sizes of bags of holding. (SRD 3.5 is my source)

D&D 4e

Thanks to help from @Carcer. It is sparse in its detail and does not mention "dimensional something" in the description.

Bag of Holding
Level 5
- This item appears to be a simple sack of brown canvas.
- Wondrous Item 1,000 gp
- Property: This bag can hold up to 200 pounds in weight or 20 cubic feet in volume, but it always weighs only 1 pound. Drawing an item from a bag of holding is a minor action. (PHB 1, D&D 4e)

D&D 5e

Bag of Holding (as 4e did) only has one size (change from AD&D/3.x)

This bag has an interior space considerably larger than its outside dimensions, roughly 2 feet in diameter at the mouth and 4 feet deep. The bag can hold up to 500 pounds, not exceeding a volume of 64 cubic feet. The bag weighs 15 pounds, regardless of {snip} Placing a bag of holding inside an extradimensional space created by a handy haversack, portable hole, or similar item instantly destroys ... (SRD, v5.1, p. 210)

As @goodguy5 points out in his concise and correct answer, you have to refer to another item to get the text that points to the Bag of Holding as having extradimensional space.
(From portable hole description)

Placing a portable hole inside an extradimensional space created by a bag of holding, Heward's handy haversack, or similar item (SRD, v5.1, p. 233)