What if there was another zero on there? How about 8 more zeroes? Still think they should need to honor the bet? They offered him $500 and tickets to a game, I think he is getting greedy.
Wouldn't it then be reasonable for them to give a refund?
It's not reasonable for FanDuel to assume a mistake there. However, if a customer purchased a bet on a game that had already happened it would be reasonable to assume a mistake had been made.
Mistakes happen and the law of contracts deals with them.