Why was this user banned from chat?

Question

Recently I discovered a user that I talked to a lot was banned for a little over 300 days. It seemed strange, so I looked into it myself. I found this chat message:

You're suspended on Stack Overflow. You should probably not be chatting in SO rooms.
You may consider that a formal warning.

He was warned by a mod he shouldn't talk on Stack Overflow chat because he was suspended on Stack Overflow. If you read a little further, you can see he complies and leaves.

However, he told me (through other means) that that was the reason for the ban. It seems to be a harsh and uncalled ban, since he complied with the warning. I seen no evidence of him talking on Stack Overflow chat after the issue. So, out of curiosity and wanting to correct a possible mistake, why was the user actually banned?

Answer 1

For rule violations.

Details of a suspension are kept private between the ♦ moderators and the user; if the user decides to disclose/discuss this in public, that's fine, but otherwise the information is not made public.

That's a site ban, not a chat ban; @ArtOfCode explains:

It's technically possible because of the chat server trifurcation and because of how chat parents work, but if you're suspended from a site then that's you being asked to take a break from that community for a while - all parts of that community, including chat.