Unless you (or someone else on your instance) actually follow that person, in which case replies should have been forwarded; or am I wrong?
@mjg59 Ah, I see. Indeed this is how one often sees posts from people one does not follow.
(One of my gripes with how APub is used by all(?) Fedi software is that they try to make it impossible to interact with the boost itself, and try to redirect all such interaction to the boosted message.)