I just re-watched it and my first impression was it was a poor stoppage. After rematching it, I am sure Bayless was looking for a break in the action to stop the fight. He stepped in when Katsidis was the aggressor and regained his legs. I was right that Katsidis hit Marquez with a decent short left backed up Marquez and that is when Bayless stepped in.

I think it was a poor stoppage because it was obvious he was thinking about the political side of the fight, rather than the fight itself.