Signs around the ride state that a rider must have two real and non prosthetic legs in order to ride. Now, it would make sense that this policy is in place to make sure that the rider is secure in their seat. This is purely speculation, I have no way of knowing what actually occurred, but if I had to render a guess, I would think that the lap bar was only touching the rider's stomach and not her thighs. I can see the riding policy being appended to include the requirement that the lap bar be touching the thighs of the rider. If this is a case, this whole incident is a matter of park riding policy and not error on the ride attendant's part.