Just stretching here but match heads make a good propellent or worse if contained. I made a cannon in HS and used match heads for propellant. Works just as good as black powder.
Did the guy have a match head bomb?
You couldn't pay me $100 to ride one of those campus buses to class at OU after what happened on Saturday... talk about a soft, easy target.. those things are jam-packed with 60+ people on each trip, with lots of middle easterners wearing backpacks for class
My personal thought is that someone dropped the matches AFTER the bench was replaced. I can't imagine the FBI/investigators leaving that kind of evidence in place.