Noooo, he hadn't responded to my last PM yet!
I have to admit I was confused as well since Calahan hadn't been involved in any recent arguments (he seems to have deliberately stopped posting in this area - see his absence from the discussion re: neeeding blood slaves for communions) and his last posts were offering map help and YARG 3 postgame commentary. My best guess is that it was because of his sig, which I note has disappeared from his posts. Honestly I think there could have been a compromise position here, remove the reference to any individual (which may conflict with Shrapnel rules) and leave it generic. Something along the lines of "because the people here are dumb-asses I prefer to discuss the game at Dom3mods."
And I think llama would have been a good person to discuss it with Cal and see if a compromise were possible.