Looks like someone bought 28k on close. You may be right that it has started. I would venture to guess that if it can break 18 it can fly to 22 as that was the gap down. Any shorts will have stop loss orders to trigger a run. Shorts have successfully beat it back on every attempt to do this since the free fall. Lets hope this time it can break that resistance.
A day like today has happened a hundred times over the last couple years. A real short squeeze isn't going to begin until it gets back to the $28-30 range. Remember the avg short entry point over the last few years has been the same as the avg long entry point: about the $20 mark. A squeeze won't start until those shorts are in the red. The stock has fluctuated between $27 and $13 for the last couple years, all the while the short interest has fluctuated between 9mil and 13mil shares, and the up periods tended to be low volume slow walk-ups, never real high volume short squeezing.