Their putting that in a message on the board does not make it a "rule" or even remotely enforceable. It's just another message.
Unless it comes from Matt, it's simply not a rule.
At the time they posted that message (before my time) the site philosophy was a bit different, and CoB's were allowed more autonomy in setting up their own rules. No longer the case and hasn't been for a long time. Since before I came back aboard.
Edit: Upon re-reading it (Thanks, Churak), I don't see the word "basher" in there. I'm a bit surprised at myself for having only glanced at the post and assumed it said so only because you said it did. That's really not my style.
I'll grant you that "disruptive posts" is subject to interpretation and the definition has been abused in the past, but that's not the case these days.