I don't think either of those have been reclaimed to the point where they have positive connotations even within the poly community ("whore" or "slut" by itself, maybe, but not with those adjectives).

Was there context? Is it possible it's an undercurrent of resentment? Either way, I'd pull the speaker aside and explain that it didn't come across as a positive descriptor. And if they can't understand that, strongly consider cutting that person loose from your world.