Just watched the you tube clip.
The way i see it is, the train was in the station, it wasnt going anywhere. The conductor could have just simply rang fo some assistance either from a colleague or the police to remove the lad.
Im sure that as a public place i.e the train, the employees or any other representative of the train company would have the right or authority to remove someone from their train if they feel the need to do so even by force if necessary (It happens all the time on football supporter trains). This is called a lawfull ejction and therefore the conductor would have had a defence in law providing it was justified and propotionate.
The Big Man in my opinion had no right to do what he did (frustrating Yes). There were no threats of violence towards the connductor or to anyone else, nor any damage being done or any apprihension that anything would have been done so.
Morally was it right? thats up for discussion, lawfully definately not.
I'm not any legal expert on the laws north of the boarder, but what i do know, is that lots of laws covered in scotland are common law and this is to protect the public against breaches of the peace. In this case, my opinion is, a breach of the peace was clearly taking place. A good solicitor may be able to argue this fact.
Being charged with an offence doesn't mean a conviction will be the ultimate outcome at court.