He's known Coombs for along time.

https://www.detroitnews.com/story/sports/college/big-ten/2020/03/02/michigan-wolverines-captain-joe-bolden-joins-ohio-state-buckeyes-coaching-staff/4929036002/

mod edit: don’t link and run.

The details: Former Michigan captain Joe Bolden is now a defensive quality control coach at archrival Ohio State. He was a Hoke recruit/player who was a captain for ttun in 2015. 
He served as a GA for ttun in 2016, and at Washington St for the last two years. 
He grew up next door to Coach Coombs in Cincinnati.