Kbin is sort of a hybrid between Lemmy and Mastodon. "Magazines" are their equivalent of Lemmy communities/Reddit subreddits, while the "Microblog" section is like a Mastodon/Twitter feed. You should be able to follow Lemmy communities and Mastodon users both on kbin.
I think Mastodon users can follow Lemmy communities and comment on Lemmy through Mastodon, too, though from what I've read the Mastodon UI isn't really set up to show Lemmy content in an organized way with good threading since its main aim is to support microblogging and following individual users. There are some things in the fediverse that you can do from multiple platforms, but will have an easier time doing it from the platform that is designed around that function.
“We’ve been hearing from creators and public figures who are interested in having a platform that is sanely run, that they believe that they can trust and rely upon for distribution,”
I think someone hasn't been paying attention to the reputation of Facebook. Between Cambridge Analytica, being used to stir civil unrest, spreading Q-anon conspiracy theories to all the boomers, and fostering an entire genocide in Myanmar, Facebook has lost a lot of trust.
I do think it's fascinating that they are hopping on the ActivityPub bandwagon though.