Thanks for the possible explanations! I used the +17% day as an example to question the short volume. Perhaps it's better to use the buy/sell ratio instead.

Fidelity showed buys outnumbered sells on that day. Alan thinks 62% were short sales, and the number should be even higher if you include the legal sells. If one believes Fidelity is correct, how could 62% of shares sold short if buys outnumbered sells?