That's interesting. Link? It definitely looked like a penalty to me, although I was only watching the video feed from home. Mark Rycroft, the analyst on the DU radio/webcast stream was surprised that it was called a major. At first, he thought they were calling a double-minor, and seemed a bit surprised by that, and actually mentioned several times throughout the game that he was surprised that went down as a major. He also mentioned several times in the third period that DU did not seem to be getting calls, possibly because they had already had more calls than Yale, and the refs don't like the penalties to be too far out of balance.
I believe that with checking from behind there is no "double minor".
It is true that a lot of the refs just want to have the penalties either even or as close as possible. It makes them feel like they didn't affect the game either way...