It's much more than that...
He has hyperflexible ankles that allow his feet to move in a much wider range of motion than yours. He has a disproportionately small torso and long legs. They have done a bunch of reports and the guy has just about every natural advantage a human could have for swimming.
Still his records and all others will be broken very soon by 'disabled' athletes with prosthetic devices that give them more advantages.
http://www.latimes.com/sports/olympi...6434101.column
Within a decade swimmers with 1 arm will be breaking world records left and right ;)