There were not that many third down conversions needed during the game as a whole, as they moved the ball pretty well with 23 first downs overall, and BYU converted 3-3 on 4th downs (meaning some third down plays were intentionally run to set up a 4th down play).

A-Rod said on Coordinator's Corner that they view 3rd and 4th downs similarly as "conversion downs" when they are intending to go on 4th. So sometimes the 3rd down is a setup play.

Viewing it as they seem to, BYU was 5-14 combined on conversion downs (even if you include the 3 failed 3rd downs where they eventually converted on 4th, but 5-11 if you exclude those since they did extend the drives). Plus they had 2 FGs on two of those. So 7-14 total (or 7-11).