"Shorts" can't vote. They don't own anything. They have sold $TSLA stock they don't own (they "borrowed" shares to sell) and the only way to close out their position is to buy back the same number of shares they sold at some point in the future.
EDIT: And even when they buy it back at some point in the future, they still don't own anything - they are just replacing the shares they previously borrowed to sell.
Mike
The way I understood the article liked up the thread is one can sell short and buy those same shares long to gain voting rights, then exit the long position after casting a vote and then take profits on the short side after the vote goes against company management.