[edheil]

Exactly what the "Antagonist" means (one character, or the whole array of forces opposing the Protagonist) is important to understanding this passage too:

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One of two situations will arise: either two *Tagonists are in
conflict with each other within the fiction, or two players are
in conflict about the direction of the story with regard to their
*Tagonists.

The difference here is important. In the former, you’re asking
for something unexpected in the fiction — the characters are
risking something in the fiction, so you want the outcome to be
uncertain. In the latter, you’re standing outside your
characters for a moment and looking at what might
be the most interesting thing that could happen to
them. You’ll probably go back and forth between
these stances, and that’s cool.

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If "Antagonist" means "whatever's opposing the Protagonist at the moment," then the former (Protagonist vs Antagonist) covers any conflict *within* the story, and the latter covers any conflict *about* the story, among the players.

If "Antagonist" means "one focal character" as I assumed initially, then you can read this as discussing the difference between direct Protagonist-Antagonist conflict and any other situation where the player of the Antagonist is messing with the Protagonist player.