Do the Unearthed Arcana Tunnel Fighter Fighting Style and the Arcane Archer Fighter's Grasping Arrow features trigger when standing from prone?

Question

The Light, Dark, Underdark! Unearthed Arcana includes the Tunnel Fighter Fighting Style which states:

[...] As a bonus action, you can enter a defensive stance that lasts until the start of your next turn. While in your defensive stance, you can make opportunity attacks without using your reaction, and you can use your reaction to make a melee attack against a creature that moves more than 5 feet while within your reach.

And the Arcane Archer Fighter's Grasping Arrow Arcane Shot feature states:

[...] The creature hit by the arrow takes an extra 2d6 poison damage, its speed is reduced by 10 feet, and it takes 2d6 slashing damage the first time on each turn it moves 1 foot or more without teleporting [...]

What happens if the creature in question is currently prone, and stands from prone? Does this activate the Tunnel Fighter's opportunity attack? Does this activate the 2d6 poison damage from Grasping Arrow?

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Note I am aware that the following Q/A already exists:

• Does standing up from prone trigger the damage from Booming Blade?

But I was told in my answer to another question that I cannot generalize answers there to conclude that standing from prone does not count as moving. So I am asking these separately instead.

I wanted to ask the question "Does standing from prone count as moving?" but was told that "There is no reason for the question "Does X count as Y?" to have a consistent, universally applicable answer." and so have asked this instead.

Answer 1

Standing up from prone is not movement

The rules for standing up states:

Standing up takes more effort; doing so costs an amount of movement equal to half your speed.

Standing up costs movement but moves you nowhere. It is not movement.

5e rules have a high degree of consistency

There is no instance where the rules say "standing up counts as movement". The verb "move" refers to movement.

You can rest assured that standing up from prone is never movement. If you think it might be, then there is confusion elsewhere.

Answer 2

Standing up is movement

Standing up takes more effort; doing so costs an amount of movement equal to half your speed.

However, it is unclear if it “moves more than 5 feet” or “moves 1 foot or more”. Either position is defensible.

However, the position that it does not trigger those effects is more defensible. Consider a creature with 10 or less speed for Tunnel Fighter or less than 2 for Grasping Arrow: they do not trigger the effects by standing while people with more speed do. This makes no narrative sense - they each stand up but the slower one avoids the negative effect?

Ultimately this is a DM call (PHB p. 6 point 3 “the DM narrates ...”) and as a player I would accept either call. As a DM, I’m ruling that while it is movement, it’s movement of 0 feet.