Does the opportunity attack from Polearm Master also proc the speed of 0 from Cavalier's Hold the Line?

Question

I wondered how this feat and class ability synergized.

Polearm Master says:

While you are wielding a glaive, halberd, pike, quarterstaff, or spear, other creatures provoke an opportunity attack from you when they enter the reach you have with that weapon.

The Fighter Cavalier's Hold the Line says:

Creatures provoke an opportunity attack from you when they move 5 feet or more while within your reach, and if you hit a creature with an opportunity attack, the target’s speed is reduced to 0 until the end of the current turn.

Does this mean if I hit a creature with the opportunity attack from Polearm Master when they first enter my reach, that also reduces their speed to 0 because of Hold the Line?

Answer 1

It does, yes. This works the same as the previous Polearm Master / Sentinel combo that existed before.

Answer 2

The Cavalier's Hold the Line works with any Opportunity Attack

The feature has two independent clauses:

Creatures provoke an opportunity attack from you when they move 5 feet or more while within your reach, and

if you hit a creature with an opportunity attack, the target’s speed is reduced to 0 until the end of the current turn.

The indefinite article "an" indicates that we are not talking about the opportunity attack in the first part of the sentence. If it were, it would use the definite article "the".