Frankly even in hindsight I would be running out of buildings, not into them. That was one hell of a sonic boom, and do you really want to take the chance of seismic activity following shortly? I would be more concerned about the building falling onto me than the meteorite.
In uncertain circumstances, I think I would almost always prefer not being under concrete.
I guess I assume loud boom = bomb, which makes me want to be behind concrete. But maybe earthquake is more likely -- it's still arguably better to be in a sturdy building than on the street near non-sturdy buildings, though.
In uncertain circumstances, I think I would almost always prefer not being under concrete.