well, low/mid rank players are known for playing with high sensitivity (which is the reason for not being very good). I mean, I play with 800dpi/1 in-game sens and would definitely not be able to do a 90degree flick (while scoped in) that fast.
I mean, 90 degree flick with awp non-scoped and THEN quickscope is normal.
But this guy first scopes in, THEN flicks 90 degrees. Definitely not something something you can do consistently and more like a lucky shot.