Yes, indeed

Nostr uses strings, ActvityPub uses JSON

ActivityPub uses inbox/outbox, nostr uses realtime websockets

Nostr lets users manage keypairs, ActivityPub manages key pairs

AP scales better, but Nostr is more self-custodial. Things like the ditto mostr bridge allow both systems to interact together, so you get all the benefits of nostr, plus the large activitypub user base.