Why not just leave them alone? Of course it is silly that they would come if the only reason was to root against BYU, but who cares.
If we want to be a top-rate fan base, we should not be booing, heckling, or being anything other than welcoming to the fans of other teams (even if that team isn't playing). If we want to be like Rice-Eccles, then keep justifying and excusing it. If I had been there, I would have politely told the guy to not be nice.