Waitin' for a train?
Lawyer up? No, worse advice ever. The police see the lawyer and straight away go harder. If your mate shows up with a lawyer then he is already admitting that there is something to defend. Don't take a lawyer, just get him to go in and answer the questions. The police are not the bad guys, they have received a complaint so they are DOING THEIR JOB, by following it up.
Probably the best advice would be to ring QR first and see if there is a penalty for forcing a train to stop. Also, ask under what circumstances a train can be stopped without charge.
Did your mate think that everyone would just have a laugh about it and call him a ######## and be on their way? QR has procedures and protocols and they are just following them by making a report. Stopping a train is pretty serious, so he has to go and explain his actions.
He was on QR property, they own a set distance either side of the track (10m I think?) and at best he would be trespassing on QR property.