Here's a crazy thought. Unlike some Bison/UND fans. Some UND fans are indeed fans of both UND and NDSU. Both fans of UND/NDSU football and UND hockey.
But from what I see most of those fans are from Fargo, went to UND, and returned to Fargo. Living in Fargo it "comes with the territory:" aka people looking to "party" without driving to GF.