Depends what race, sanctioning body, and rules that were in place.

For IM, Athlete A has ~25secs (I believe that's the time limit) to drop back. Athlete B has to move over to the right once passing, otherwise they can be given a "blocking" penalty. So, technically both athletes could be committing rule infractions and receive penalties.

Is there a draft in that position, depends where the wind is coming from?

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-Brad Williams
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Lateral position isn't part of the equation. A is drafting if he doesn't drop back and B is blocking if he doesn't move to the right after passing.

 Athlete A is overtaken by athlete B. Athlete B's lateral draft zone is wide of A, but A does not drop back. Is that drafting? //

Yes, that is drafting once you have used up the allotted time you are allowed to drop back..