Do the spells from the drow commander's magic bolts in "Against the Giants" (from "Tales from the Yawning Portal") require concentration?

Question

In Tales from the Yawning Portal (p. 209), in area 20 of the Hall of the Fire Giant King (in Chapter 6: Against the Giants), there's a variant drow elite warrior who is mentioned as a commander, and has three magic bolts. The text reads as follows:

[...] The commander has a +2 shortsword, a +1 hand crossbow, and three magic bolts, as follows:

• A bolt of holding, which casts hold person on a target hit with the bolt, as well as up to two other targets within 30 feet of that target
• A bolt of blinding, which casts blindness/deafness to blind on a target hit with the bolt, as well as up to two other targets within 30 feet of that target
• A bolt of vapors, which casts stinking cloud centered on the point it hits

Each of these effects has a spell save DC of 15 and a duration of 1 minute.

Does "casting" Hold Person and Stinking Cloud like this require the drow commander to maintain concentration on the spell?

It seems too powerful for a CR 5 creature to be able to paralyze three creatures in a single action without concentration.

Answer 1

No

The rules state:

Using a magic item's properties might mean wearing or wielding it. ... A weapon must be held.

These bolts must (presumably) be fired from the previously mentioned +1 hand crossbow and each "casts X on a target hit with the bolt" and explicitly have "a duration of 1 minute."

Who's casting the spell?

These can be distinguished from items that "allow the user to cast a spell from the item" and force "the user of the item must concentrate if the spell requires concentration." All items that allow you to cast a spell explicitly say "you cast" - these items don't say that, they say the item casts.

The items themselves "casts X on a target hit with the bolt"; they do not "allow the user to cast a spell from the item."

Are these Concentration spells anyway?

The rules say in respect to spell casting items:

Certain items make exceptions to these rules, changing the casting time, duration, or other parts of a spell.

These items change the duration from, for Hold Person, "Concentration, up to 1 minute" to "a duration of 1 minute."

These items, therefore, do not require anyone or anything to concentrate.

Answer 2

No, the ability specifies what the duration is.

The stat block specifies:

Each of these effects has a spell save DC of 15 and a duration of 1 minute.

The specific duration of "1 minute" overrides and replaces the duration of "Concentration, up to..." that these spells normally have.

Is this overpowered?

No, not really. Monsters often have one-shot abilities that would likely be broken in the players' hands.

Anyway, there's a lot of ways for this to fail. Consider how much has to go exactly right: First he has to hit with the bolt (and he only gets one try); then the targets get to save against the effect, and then anyone who fails gets to save again each turn (standard for hold person). Are the players going to lose several actions? Yeah, possibly, but it's unlikely they'll be so badly disabled that it makes the whole fight go sideways.