Good question! I'm sorry I left out the details. Yes, it is the caffeine and the book I followed (The Renegade Diet by Jason Ferrugia) recommends 1 cup about 30-45 mins before the workout to burn fat even faster.

Even though I now rarely work out before going to work, I still start my day by drinking a glass of water and then a cup of coffee and it still feels good :) If you drink decaf, I think it would have no positive (but probably also no negative) effect.