A quick google search shows that although it’s not common, you can develop color blindness for a number of reasons later in life. It’s possible that’s what happened. I know a guy who had an AME for years in Florida that never did an eye test of any kind. Many people used that AME. People went to him from all over the country. Eventually he was busted for basically handing out medicals. It’s possible this guy was in a similar situation and finally had to go to a legit AME that gave him a real eye test. It’s also possible he’s full of crap and deserved to be fired. It does seem really fishy but if this guy is smart enough to get hired at United, wouldn’t you think he’d be smart enough to realize how fishy this would look and he wouldn’t do it if it wasn’t legit? The truth will (maybe) be revealed at some point.