So, I guess the question a jury will have to answer will be: Was this passenger being denied boarding even though he had already boarded? What's the correct definition of "boarding"?
That is the key I think. When are you actually “boarded”? In honesty, it is this kind of stuff that has kept me from flying the last number of years and when I did, I avoided American airspace whenever I could (taking direct flights from Canada)
I flew standbye within Canada for 10 years to save money and I knew the rules and was treated always with respect even when I was denied boarding (at the gate). The airline staff always felt sorry for me because I was always there early just waiting to see if I could get on. Always the last to board and often didn`t get a meal because it was cancelled. But I did get toast and jam. lol
I would think his lawyer will argue that when his boarding pass was validated he was boarded.