To understand the principle is not the problem. ;-) But if you look at the chart and the volume at Bittrex, you will see: The person who sold 5000 Neos around 17k could not buy back this low or even lower. And maybe the selling was just one person. And then he would have sold more than 10000 Neos. And all lower than 20k mostly lower than 19k, some around 16k.
Then we just lost somebody that just could not wait, I do think it was one whale trying to change the price to get back in. The charts are not readable for NEOS, the bottom is 20k so that person is hoping for the best and might not get back in