ADI on the back burner, page-105

Yes, I think it is reasonable to say the shorter is a non-holder, whether or not they took possession of the stock briefly before shorting. It's pretty unusual to take possession as an end user, but either way, non-holder is the appropriate designation in my opinion. @centro11's view is in line with that too.

Another way you can think of acquiring stock for a normal person is that you always have to give something in exchange. If you buy it, you give money. If you borrow it, you give an agreement to return some equivalent stock at some unspecified future date and give the lender some collateral as security against the stock loan. Either way, you get stock and you gave something in return. You very definitely own the stock in both cases (not for long if you're selling it though!)