I don't know about others, but I've had amnesia twice and both times I only lost access to my personal memories and personal facts. Any physical skill I had I could still do, walk, talk ect, and generic facts, I knew a tv when I saw one, a carpet ect.
So based on my personal experiences I doubt he'd forget how to glide, there there may be some rare brain conditions that may explain how, I doubt the writers of the script were planning on that since I would doubt they call up brain scientists to ask if there is a condition that can cause x.