I'm genuinely surprised that no-one they filmed (or showed, anyway) booed him to his face, if that's how they react to a cardboard cutout. At a football game, ex-players get booed to their face, so what's the difference? Is it merely the strength in numbers of fellow fans when people do it at a game?
I wouldn't boo a player in that situation because, if the roles were reversed, I'd probably do exactly the same thing and move for more money, etc.