That's certainly one suspicious bet. If the guy would win that bet, that would most probably be investigated by the bookie's security department. I can't think of a reason why the guy made this bet and why he considered it safe? Was he drunk or high?
I disagree. There is nothing suspicious about it frankly speaking. The bookie's security department wouldn't bother investigating such bets since it clearly looks like a legit bet.
That gambler thought this was a sure bet just like many other gamblers and never expected a comeback in the 2nd half which is why he thought that it was easy money, but luck turned against him and screwed him over.