You have to realize that the Mesa/Gilbert/Chandler area has one of the highest concentrations of LDS people in the entire country outside of UT/ID. It's almost a like a southern extension of UT county.
For this reason, it has a lot of LDS people who dislike BYU for the same reasons ALUFs dislike BYU (elitism, sour grapes from past experiences or rejections, disenfranchised with Church, etc), and then you have a bunch of non-LDS people who for some reason find it very annoying to have so many or those troublesome Mormons in their town, and associate BYU accordingly.
It really is that simple for the folks who have particular feelings about BYU, and has nothing to do with a sports rivalry... yet.
For most folks though, I think it was just another big game, which a ranked opponent, with conference championship and playoff implications. They also have an earned reputation for rowdy and intoxicated co-eds in general, so you can't read too much into that. 19 and 20 yos are what they are, but not that specific to BYU, per se.