It was just an example of that sort of thing- we've all seen similar creatively-worded job titles.
So not so much "Urban myth" territory, more an understanding that a casual post on an internet forum needn't be held to the same standards as a peer-reviewed journal.
So you just made it up basically.
Anyway, to get back on topic. Years ago there were Guards in most (all?) settings, though even then there were distinctions between passenger guards and goods guards.
With the arrival of paytrains and the development of a commercial role [my recollection from the 1960s is that on long distance trains any ticket checking on-train was by Travelling Ticket Inspectors rather than Guards] the role of Conductor / Conductor Guard was created. Then Senior Conductors appeared, largely - I suspect - to give greater status for the bloke (and they were almost all blokes in those days) on the 1130 Euston - Glasgow over the bloke on the 0652 Stoke - Manchester stopper.
This was further upgraded to Train Manager for what had been Senior Conductors; again, I suspect, a status thing. To be fair, the guy who takes charge of all passenger-related stuff on an 11-coach Pendolino from Euston to Glasgow probably merits a better title than Conductor (even with the Senior prefix).
It's also worth pointing out that the term "Conductor" which would have been widely understood in the 1960s/1970s to be someone who would sell you a ticket (on a bus) would be rather less familiar now since bus conductors are vanishingly rare these days.
Of course, in Manchester bus conductors were known as Guards, but that's Manc for you.
