If he can BET that much, what kind of money does he HAVE?
In the opinion of many psychologists, the major thing about gambling is that it is only fun when he amount bet could mean a loss that hurts.
Somehow, I doubt this would hurt him as much as a $100 bet would hurt me, but...my guess is a loss of that much WOULD hurt.
Don't be surprised to find that he places a bet in the other direction if the spread changes during the next day or two. And a huge bet like that might effect the spread somewhere. Having just "the middle" of two bets is a great place to be.