It's a good question, and I agree, one I should have asked.
I can't speak for Professor Noel, but there were about a dozen Democrats in the Senate in 2010 (mostly from red-states) that wouldn't support the bill. (I outlined them in this post.) So on this issue, the Democratic party and the liberal ideology weren't perfectly alligned.
But on the other side, there weren't any Republicans that would support the bill. So the Republican Party and the conservative ideology were perfectly alligned. That's why 60 Democrats in the Senate didn't lead to 60 votes for cap & trade.
It certainly is more complex than just ideology. But ideology does seem to be a major factor in how Members of Congress are voting.