I think the notion that Yale is a huge underdog is solely driven by their implosion in the ECAC playoffs, and the subsequent fall to the 15th seed. If you go back to the Friday afternoon that the ECAC playoffs started (just 11 days ago from today), Yale was tied for 4th in PWR with Miami (QU-1, Min-2, UML-3, Yale/Miami-4). After completely laying an egg against in Atlantic City, they fell all the way to 15th and barely made the tournament.
If you consider their no-show that weekend to be an anomaly and you take their season long perfomance in context, up to that point 11 days ago, and putting any stock in the Pairwise at all, then their win vs Min was in reality a very minor upset (PWR-4 beating PWR-2), and their win over North Dakota wasn't an upset at all (PWR-4 beating PWR 7 or 8).
I fully realize that you can't just exclude games and say that they are the 4th ranked team in the country and Atlantic City never happened. What I'm trying to illustrate is that 11 days ago they were 4th, and thus they are probably better than the 15th seed indicates. The 15th seed is what drives the "major upset" talk when in reality they are probably close/equal in talent to most of the teams in the tournament.