One point of confusion between Nostr and Pubky is that Nostr signs individual events (the post-it notes) while Pubky just signs the pkDNS (the board where the post-it notes are stuck on).
On Pubky you could build a client that signs the post-it notes and not just the board. It's just that if you can sign the board then there's less of a need to sign the individual post-it notes, hence the demo client shies away from that.