I've heard it frequently enough that I mostly believe it, but everywhere I look, it seems like he cites distance from home as the big reason for choosing BYU over Boise St, not the schedule.
I know he had an offer from at least Cal as well and skipped a visit to Iowa to commit to BYU, so I can't imagine it's only about being able to play a stronger schedule since those teams obviously do play P5 schedules. And Cal obviously has a pretty strong recent QB history with Aaron Rodgers and then Goff #1 overall.
From Desert News:
https://www.google.com/amp/s/www.deseret.com/platform/amp/sports/2021/1/3/22195624/byu-football-zach-wilson-lds-mormon-heisman-finalists-nfl-draft-2021-john-beck-3dqb-camp
Zach said as a four-hour meeting with Sitake was winding down, the coach mentioned something that resonated with the young athlete, a self-described “big family guy” who loves eating his mother’s home-cooked meals.
“He said if I came to BYU I could drive home every Sunday night and eat dinner with my family,” Wilson said. “That meant a lot to me.”