But how can he take such a risk by wagering $1.4 million just for a net profit of $11,200, which is 8% of the total wage if he had won?
0.8% actually

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.
It's really the opposite. These type of bets are made thousands of times every day, not for this amount of course, but for 100x this amount if you counted up all those bets.
What exactly would they investigate? It's an NFL game, the most unlikely of all games to be rigged.