With the caveat that it wasn't one of the wretched teams they've occasionally scheduled lately. I don't know what actual Utah support has been this year, but I was at the Colorado game, and there were definitely a lot of empty seats, in spite of the "sell out" they announce.
I don't think BYU's support is as strong as it used to be in year's past, of course, but it's still relatively strong compared to the strength of it's football team.