I once got told off on an EMR service for having a ticket from Bedford to St. Albans City as I "was supposed to be on Thameslink".
So I explained that I knew this train didn't call at St. Albans and I was getting off at Luton. Expected that to be the end of it, but nope. I was then told that I was going past St. Albans to come back to Luton, and that wasn't allowed. The inspector's colleague had noticed she'd been with me for longer than would be normal, so made his way down to check everything was OK. At this point the inspector realised her mistake, apologised and that was the end of it. Her colleague arrived and asked what was happening, she explained and the three of us had a laugh about it and they moved on.
Almost certainly human error in this case, as alluded to above. I would expect RPIs to have a reasonable knowledge of their usual patch, but they may well get deployed elsewhere, so wouldn't be as familiar with other areas.