It can't possibly have an airfoil. That's got to be a purely symmetrical airfoil shape, otherwise it'd be flipping him over forward violently. I didn't believe this design at first sight, and when I saw it actually flying I was amazed at how dangerous it was. It's basically an air surfboard. Astonishing. The weight distribution is nuts, I can't see how he'd possibly regain control if it flipped backward or forward even once. It'd just tumble out of the sky with you on it.
You would use an airfoil suitable for flying wings. They tend to curve up at the back. One of my gliding instructors used to fly this flying wing with reasonably good performance (35:1 glide ratio):
Note the comment about the narrow centre of gravity range. The instructor said that wearing his heavy boots would change the flying characteristics enough that he could notice.
So such things exist and are at least somewhat practical.