Why why why do we keep obsessing on short interest? Has it helped anybody?
One reason the information is of interest to me is simple supply and demand. The data
@vgrinshpun posted suggests that expanding the supply of available shares by 2.5 million via shorting would have neutralized the effect of buyers who bought 2.5 million new shares, which otherwise would have exerted upward price pressure on the SP.
You can look at that in a variety of different ways, but in my mind it certainly helps explain why the SP has not increased despite what I believe to be objectively good developments over the past several weeks -- especially the ER.
Shorting in the face of
good news and a flat share price also suggests the possibility that short sellers are manipulating the SP to avoid an upward move as
@Papafox has theorized and documented.
One thing that I don't think I have seen mentioned is that making risky short bets on shares to defuse upward pressure on the SP would make even more sense for hedge funds who have made bigger bets through leveraged options. It would be worth risking a little money on the underlying asset (the shares) to protect against much larger losses on options. Michael Lewis gave an example of this in the mortgage derivative markets in
The Big Short, although in that case the price of the underlying assets were (allegedly) artificially propped up to protect against larger losses on the derivatives instead of held down. That worked great. Until it didn't and the mortgage market came crashing down and the parties holding the derivatives got crushed.
Shorting into good news, if that is what is happening, is a very risky move for short sellers because if the good news continues and they are eventually forced to exit their short positions, the decreasing supply of shares should accelerate the price increases that would otherwise occur. On the other hand, the strategy could succeed, especially if they get bailed out by Tesla stubbing its toe in some way, negative macro developments, successful manipulation of sentiment, etc.
Also, manipulation of the SP is not the only possible explanation. It could be as Ihor D suggests that shorts actually believe the ER was bad news, or the shorts could be making a momentum play, etc. I personally don't find those other explanations very convincing at this point.