And if this headline used Train hero as a name (e.g. Train Hero) rather than a description of a person then we'd be closer to a one-to-one comparison. If they used the train hero's name in the headline in addition to calling him hero, then you'd be spot on.

Even then they wouldn't be scare quotes. It would just be a different style choice. I checked the BBC style guide and this is pretty open to interpretation.

No one at the BBC is making a case that an unarmed man stopping a mass shooter is not heroic. This is people looking for stuff to be outraged about.

Yes. In this case it's the author of the article calling him a hero. Rather than a person he has quoted. 

I mean, obviously I'm being a bit rude, welcome to the internet. But quite literally this gets asked and answered all the time. Quotes in newspaper headlines in Britain are literal quotations of what someone said to the reporter, in the article you may choose to then read below. 

That's how the system is set up, there's rules and order and we don't need to worry all that much about the presence or absence of quotes except to delineate exactly that