I'm sorry to disagree, but I promise you that at least the strong extroverts would be happy to talk to somebody at least. Just by the numbers that should make up and not too small part of a train passengers. Plus it is easy to wander around or pretend to exit on the next stop in case the situation gets too awkward.

In fact I would argue that this is exactly the right social environment for practicing social skills as it takes place outside the typical peer groups and "save" settings. In a setting where people know somebody already a sudden change in social interactions might come across as weird and odd. The same thin a train is totally random and chances are super small to meet these people again.