I guess the question is whether the time of 2 1/2 hours is the raw driving time on the road, or if it includes all the other things that take time (such as getting from the classroom to the car, making the side trip home, taking care of biological needs, being driven from home to the airport, reasonable consideration of possible traffic delays, etc.)
I would make sure that everything that can be done ahead of time is done, such as having a full tank of gas and not having to do anything at home aside from getting into a different car.
Detroit is a huge airport. The time to pass through security is an unknown variable. Flights start boarding 30 minutes before scheduled departure.
If he's dropped off at the curb 90 minutes before departure, boarding pass in hand and no luggage to check, he'll be fine, even if there's a long line at security.
But if the 90 minutes gets whittled down by 10 minutes here, 15 minutes there, and 20 minutes someplace else, then he could get to the gate too late.