It wouldn't surprise me if someone did get fired. I just think about how there is so much repetition in the daily life of someone who works in the boarding process that the times I have been there they don't really seem to be paying too much attention to what you are handing them. Perhaps they kind of depend on the computer to do it for them the same way that all of us rely on GPS rather than having some idea where we are going when we drive.
It does seem a bit silly that the passenger would be so oblivious as to what was going on around him though. Maybe he was one of those guys that we frequently see that has his Beats by Dre headphones on all the time and isn't paying attention to their surroundings at all.
RE: Man boards the wrong flight... goes 1400 miles in the wrong direction