@top@top.ofthe.top @equipo@red.niboe.info It's a Mastodon "feature". I investigated it a bit here, and found this ticket where it was proposed/added. TL;DR is that each Mastodon server indeed notifies all servers it knows about, about all deleted users.

Also worth noting that Mastodon has implemented a "shortcut" for them: when receiving such activities, they promptly ignore them (otherwise, they would request public key for this user).