Being a good top is probably more about reading your partner's signals and really being able to take them where they want to go than how to thrust, but....
This guy is using his lumbar / erector spine to roll his hips and get a rhythm going. It's mostly hip flexors and a good dash of lower back control involved. If you're looking for some exercises to support this specific type of thrusting, I would look at stretches to keep your hip flexors limber (getting sore from being in this crouch position is a bitch), and exercises that are meant to strengthen your erector spinae.