It should have been left to the transport police. I get why the guy decided to take things into his own hands, I'm sure we're all sick to the back teeth of the level of rudeness to strangers that seem to be the norm these days and I'm not targeting the youth with that either.
The guy effectively chucked the teenager out of the train, his bag, his meds and I assume his phone, were all left inside the train so how was he going to get home or at least contact home to make alternative arrangements.
They're both in the wrong IMO.