Could you please explain how a Lemmy thread is showing up in Mastodon? I use it too but never see Lemmy there.

Isn’t that just a Piefed photo stream?

I still don’t see any cross-app integration except simple linking.

Can you be more specific? I don’t see anything.

You’re not the first to suggest it, but I still haven’t seen anyone do more than linking one from the other. This feels as inconsequential as posting a Twitter screenshot on Reddit. Is there a deeper integration possible?

Communities are for Lemmy and hashtags are for Mastodon.

They each make sense in their proper context.