Polymorph into snake interpretation

[Legion98]

In Volo's Guide to Monsters, the Yuan-Ti "Unusual Abilities" section (p. 98) lists a number of action options that might be given to high-ranking yuan-ti, one of which is:

Polymorph into Snake (Abomination or Malison Only; Recharge 6). The yuan-ti targets a creature it can see within 60 feet of it. The target must succeed on a Wisdom saving throw or be transformed into a Tiny poisonous snake, as if affected by the polymorph spell. The save DC is the same as that of the yuan-ti's Innate Spellcasting ability.

It's not stated that you cast polymorph; it says that the target is transformed "as if affected by the spell".

What's "as if affected by the spell" means?

Is the yuan-ti casting polymorph?

And if it's not a spell but a "special trait":

Does it requires concentration?

What's its duration?

[Spectrulus]

What's "as if affected by the spell" means?...

Given that the entry also references the monster's Innate Spellcasting Ability, I would argue that it follows those rules.

This would mean:

Is the yuan-ti casting polymorph?
Yes.
And if it's not a spell but a "special trait":
It is an Innate Spellcasting Ability.
Does it requires concentration?
Yes.
What's its duration?
Up to one hour.

[JackPhoenix]

Is the yuan-ti casting polymorph?

No. The end result is the same, but it's not actually a spellcasting... no components necessary, unable to be counterspelled, etc.

Does it requires concentration?

Yes. While it doesn't originate from a spell, the effect is the same.

What's its duration?

Concentration, up to 1 hour, just like the spell.