There are better ways you could word the announcement that don't humiliate and still get the message across though. That would be my complaint.
Barring a genuinely outrageous announcement, such as one that was overtly sexist, racist or homophobic, I think if you've done something that was definitely wrong, you knew it was wrong, and it was made clear on the PIS that it was wrong, then an announcement along the lines of "Ladies and gentlemen, please note that smoking is prohibited on this station, this includes the man in the yellow jacket by the escalator, yes, you" is a totally reasonable way to deal with the issue. I've heard that sort of thing a few times.
The thing about a PF is tripe because they are not a PF TOC (though I seem to recall something in the new NRCoT would legitimise the sale of a single from Newcastle, though I forget what), but describing the offender (so they know it's aimed at them) and asking them to leave seems totally reasonable to me. They might even be helped by a passenger assisting them to leave so the train can proceed - this is a classic London bus driver tactic to get a non-payer off without risk of assault.
You'd get the exact same thing if you boarded a southbound Avanti at Watford. Those ones aren't about timetable efficiencies or being able to depart early, they're because the TOC gets no revenue and thus doesn't want to carry you for free.
If the OP wanted a ride on Lumo for a ride on Lumo's sake (which I guess he did) a quick polite word with the guard (or whatever it is they have instead) might have resulted in him being allowed on anyway.
I’ve never felt so humiliated in my life.
With all due respect, you were doing something you weren't meant to do, you knew you weren't meant to do, and if you didn't the PIS was telling you you weren't meant to do it. I don't think that announcement was impolite. It made it clear they were asking you to leave, and presumably you did.
The bit about a PF was nonsense, but if you're going to break the rules you do need to accept what might happen if you get caught, and a slightly pointed announcement is down the low end of things that might happen.