This is not correct. If the dog is +640, the favorite is not going to be even money, it will be minus quite a bit. For instance, currently Sunday to bet on the Browns to win you get $205 for $100 if they win. However, to bet the Ravens to win, you have to bet $250 to win $100. Tonight on our game, if you bet NMSt to win for $100, you would have gotten $1400 if they won. You would have had to bet $5000 to win $100 if you were betting Kentucky to win.
Re-reading your post, we might be saying the same thing. If you are saying the favorite was -700, we generally agree.