Sure , it's a plausible
explanation
If he punched the driver truly because he wanted to protect the
girl, if he really felt that the driver was being rough on her,
believe you me that would be the boy's first line of defence when
speaking to the press
Attack the driver's actions, justify his own, rather than go on
defence! That's what any sane person who has confidence in his own
actions & can account for it, will do.
I also believe that if the driver did something wrong, eye
witnesses would have mentioned it.
Oh well, time should reveal more details