Banning somebody for a rule that they don't know about? I doubt the moderators have gone that low.
There's three kinds of rules:
The Forum Rules - The rules of the particular forum you are using that you must oblige by in order to be a good member.
The Implied Rules - The rules that should already be known without saying.
The Contingency Rules - The rules that you should know from past experiences
and should not break for they might be used in the same forum.