Follower counts are really broken on Nostr because of the decentralized nature of the protocol. Maybe not broken, working as intended, but hard to gauge actual numbers. It's why we joke that it's not a good metric here. That said, Primal indexes all followers across a large amount of relays. Most clients don't do that. Primal will show a completely different number than another client. Amethyst for example would count follows based on your relays.