This is something with nostr that I’ve never quite understood. If I create a note for it to be seen, I and the other person have to share at least one relay in common? Are there any main relays that pretty much all clients and users use as one of their relays? 
Probably because you were part of a conversation that was getting federated somehow. I’m not sure how to get on the list. Maybe someone on the nostr side has to follow your Fedi account.