I happen to know a little about this issue.
In American law, the courts will generally uphold “click-wrap” licenses, where the website forces you to “click” that you accept the terms- even though nobody reads it.
A situation like this one is much more shaky. If it didn’t say anywhere on the screen that there are rules, I would say it is pashut there is no contract.
But it does say “RULES OF THE CR”. So maybe this is different than Specht. Who knows. (What if you clicked on a link from the main page straight to a thread, and never saw the rules? Who knows?)
I was questioning above whether under Halacha there could be a contract, since there is no kinyan. That may have a clearer answer, but I don’t know it.