I like to try to think about it from the MMs perspective:
If I believe a stock will be seeing a huge surge of demand in the near future, my goal is to grab as many shares for as cheap as possible. This is especially easy when you have a low volume & low float stock, like HGEN. Take the share price down 5-10% off very little volume and trigger stop losses and get fearful investors to sell thinking "someone must know something" to create the market for me to grab cheap shares.
If I believe the stock is going to see a decline in demand/value in the near future I want to rid myself of as many shares as possible for as much $ as possible - if you create FOMO by taking the price up, a surge of retail buyers hoping to get rich quick off a upcoming catalyst inevitably flows in creating a market for me and my institutional friends to get rid of our shares for a profit.
Look at VXRT for a recent example of FOMO buying before data release. Stock ran up over 200% in the weeks before a bad data release. I swung that one in two weeks from around $9 and sold at $22 day before release - admittedly I was a little lucky with my timing there, but my gut told me the MMs were up to no good.