It's mostly about what relays each app is using to look for who has you in their follow list.

On Damus, it may try to check as many relays as it knows exist to try and find your follows, or a set list.. Not sure. Would be a question for nostr:npub1xtscya34g58tk0z605fvr788k263gsu6cy9x0mhnm87echrgufzsevkk5s or nostr:npub13v47pg9dxjq96an8jfev9znhm0k7ntwtlh9y335paj9kyjsjpznqzzl3l8 .

Primal, on the other hand, just checks its own massive caching relay, which in turn pulls notes in from a large number of other relays.