I'm not sure I would call that pass under-thrown. If the defender (Hood) hadn't been in perfect position, the ball would've hit the receiver (Matthews) on the hip.
Could it have been higher? Sure. It could've arrived at his shoulders. It could even have been above his head when it got to him and still been catchable. All of that is a good throw.
For me, "under-thrown" means the receiver would have to break stride or even stop his route to have a chance at the ball. If it arrives in the target area defined by the circle his arms make when he swings them 360 degrees, and he's still flat-out running the route, that's a good throw. Might not be shaded to just the right place, but it's not under-thrown.
Main point is, don't make digs at the QB's throw when the primary reason for the interception is the DB putting himself in the perfect position to make a play.
Good on Hood.
Go Vols!