I hate that this is how Bosa's college career ended, but that is absolutely the right call. The rule is in effect not only to protect the offensive player, but the defensive player. Bosa led with his head there. Tackling like that is what leads to serious head and neck injuries for the tackler.
Bosa will be a top-5 pick in the 2016 NFL Draft. There is a decent chance that he ends up on the Titans. Lambert is already working up a scouting report on Bosa that should be posted tomorrow night.