Look at the list of his competition:
How many of those names are players you even remember ever playing.
Rocket Ismail and Dave Klingler. and Klingler had a lot more TD passes and fewer interceptions.
And not to take away anything from Ty, he was an amazing player. The Miami win did a lot to put him ahead of everyone else that year, and he was also riding the prestige BYU had, that was built before him by Wilson, Mcmahon, Young and Bosco.
And it was clear to the voters he was #1, the 1st place votes across all of the voting regions confirmed that. But the game was different then, and stats like that today wouldn't carry a player very far, unless he was riding an undefeated or 1 loss season and had some very good wins. (Which Ty did have that year, as BYU had the Miami victory and only the Oregon loss as all the votes were in before the bad Hawaii loss, and BYU was ranked #4 in the country at the time).