I did "pick one line" because it was a contentious (and apparently anti-passenger) one! Yes, we may well know many possible reasons why door release wasn't effected, but, my point was that a passenger cannot be expected to know (or care) about such niceties. He and all the other people waiting would just want the doors opened to gain access and sit down. Who is to say that he "knew full well that the doors would be released"? If that hadn't happened one minute prior to scheduled departure, questions would obviously be forming in passengers' minds. The average passenger, seeing a member of staff in the cab, might well ask if the doors could be opened, without being labelled as nosey.
As I said, I was not commenting on this specific incident, but simply pointing out that passengers often are left wondering why access to trains is denied to them. I have no idea what was said here (as I also pointed out), but it would seem that there is more to it than we know so far.