We can't see much of anything. The image shows all of 4 comments. But I can guess, considering the all capital username and copy-paste format - I would bet money that they posted that same thing over and over again. Also, I know this platform is understandably anti-Reddit, but I really doubt they're banning people for a single comment about Lemmy.
I'm not defending the Spez stream. I'm saying spamming a chat with JOINLEMMY is just going to make Lemmy look bad and associate it to new people as an annoyance rather an interesting alternative.