Here is the video of him bowing. When seen from the side, can see his foot slide back as his head goes down.
http://www.suntimes.com/news/politics/obama/1518581,w-obama-saudi-king-bow040809.article
“It wasn’t a bow. He grasped his hand with two hands, and he’s taller than King Abdullah,” the aide was quoted as saying by Politco.com Wednesday.
You can see in this video that Zer0's left hand is tucked into his own waist as he "leans deeply towards" Abdullah. Stop it at about 0:12 seconds and you can see his hand flop impotently down to his knee as he begins to come back up from his "deep lean towards" Abdullah.
Isn't putting your left hand on your abdomen at the waist as you bend forward a traditional part of bowing?