Bottom line is, the conductor should have said to the chap "please leave the train.." or even better had some patience with the customer and tried to discuss the situation. When he refused, he should of advised him, "I'm sorry sir but I'm going to have to notify the authorities and you will be removed from the train.." then carried out the correct procedure.
What I've just written is very easy to say, and takes no longer than 2 minutes. But that would make the Conductor feel like he was losing face, hence the repeated "OFF!!" that can be heard.
It is not his job to physically challenge or attempt to remove him himself, which is what happened, as it was a catalyst for a member of the public to then 'protect' the conductor with rash behaviour. Why didn't 'Big man' speak to him first? He saw this as a public opportunity to display his strength and power to carry out tasks that others couldn't, and also probably wanted to get home. But would it have been that hard for 'Big man' to try and reason with the lad if he really has to get involved.