I guess some smart shorts covered just now. The volume was not so big, around 100 to 200 thousands have been covered. Such a small amount already caused a spike. Imagine 41 millions are shorted. Even without a squeeze, the share will go back to the high 30s range at least, if they all cover and if longs hold tight.
"The short ratio (or short interest ratio, SIR) for a public company is a metric signaling prevailing investors' sentiment. The ratio is calculated by dividing the number of shares sold short by the average daily trading volume, generally over the last 30 trading days. The ratio represents the number of days it takes short sellers on average to repurchase all the borrowed shares. The ratio is used by both fundamental and technical traders to identify trends."--from Wikipedia