Correct. They did not lose a non-conference game. Their main non-conference schedule was the Phil Knight tournament - they beat Oregon, Alabama and Iowa State. They also beat Oklahoma State at home and Florida on the road. They had a really bad stretch where they lost 5 of 6 starting New Year's Eve, then they largely righted the ship.
One can make a good argument that the Big East was the best conference this year. Sure, there was some degree of self-promotion there (which all of the coaches are doing this time of year, so I don't have any problem with that), but one can also make a legit argument in favor of that. I hope I am not now setting off a long thread of battling meaningless statistical metrics about which conference is best - I will trust my eye test and NCAA Tournament performance on this one...