@montecook The easiest way to think of it is like this: ActivityPub is made up of information that various applications PRESENT differently. A Friendica (Facebook) account might have posts, pictures, and events. But if someone on Mastodon follows a Friendica account, Mastodon might not know how to interpret events since it doesn't have those. Events might turn into oddly-formatted toots (the nearest equivalent).
Lemmy is basically Reddit threaded discussions. Those don't translate well here.