I'm very suspicious of this. Not of them, but you, I'm afraid.
Too much detail, which you can't make your mind up about. "Or don't have valid tickets" - I'm afraid I think you're making this up.
Too little detail, you're a trainspotter / train enthusiast, you'll know exactly the sort of train you're on and how "long" it is.
Firstly, I wasn't making this up.
When I travel, especially on InterCity services, I wear large, noise reducing headphones. So, I've heard the phrase "Yeah, but it's so crowded the guard won't come down so we don't need to worry" (roughly) with headphones on. I then removed my headphones. One person was on the phone to their mum and made the same comment. There is absolutely no reason to say that unless they have no or an invalid ticket.
I didn't go into details of the train I was on, because I did not want to identify the train I was on, certainly not at the time. I can do into some detail now (HST, full East Coast formation minus coach D, first class had unrefurbished seats in coach L).
Now, even though I wasn't making it up, would it matter if I was? This thread has and will turn into a discussion about if non-railway staff would tip staff off about fare evasion. That is quite an interesting and useful railway discussion.