Same users posting same content on all instances - eviltoast

I’m just getting familiar with lemmy fediverse and trying to make my way through it after getting out from reddit. I’m trying out liftoff app for android and I’m seeing way more double posts from different instances from same users. Same content from same users on multiple instances. I thought fediverse supposed to, You post in whatever instance you are and it’ll be shared among all instances. I’m more confused now.