it is not flash crash
It is exchange manipulation to trigger stop loss on MT4 trading platform with leverage. it is not first time happens, allows exchange to take 85% of the deposits instead of 0.5% of commission....
watch this, it in russian, but watch it from 2:40, "Hunt on stop loss", this is the backoffice of the MT4 platform, allowing to manipulate and trigger stop loss:
https://www.youtube.com/watch?v=p0JInOpEVfw&app=desktop