It is remarkable, but a little less so when you take a closer look at who the 21 wins have come against.
5 FCS teams
5 P5 teams(Pitt, GT, Mich, Mich, IU)
11 G5 teams
The 5 FCS teams are gimmes, so no big deal there. The P5s are tougher, but 3 of them had losing records(Pitt, Mich, & IU); only GT and one of the Michigan teams had winning records.
As a member of a P5 conference, the 11 G5 wins are to be expected especially the 4 wins that came against G5s with losing records: Fresno, Fresno, USU, and SJSU. That leaves 7 wins over G5s with winning records: BYUx5(which is impressive), CSU, and USU.
For comparison, before joining the Pac-12, Utah was 22-7 in non-conference games under KW.
11-5 vs P5
9-2 vs G5
2-0 vs FCS