I also have no clue. I read the rule book further last night, turns out the NCAA is a bunch of fools, shockingly. After it says you can't play with one goalie there's a section a page or so down that says you can play with one goalie. Who the hell knows.
I poked around some of my friends within the athletic department, BU did not want that game cancelled. They're already teetering on the minimum games limit and their season not counting. 100% wanted to play that game and still do.
So none of this makes any sense.