You are braindead.
1. If you actually watch the clip, u can seem him get flashed in 3rd person view (the player models hands cover his face).Which is why he turned also.
2. You can see where the flash popped, he is 100% full blind, not partial.
3. You clearly don't how how buggy flash assists are. You only get it when the person flashed is still partially blind. - SO if you get flashed and get killed, and the second after you are no longer partially flashed you wont get the assist flash.
Maybe if you played CS, you would know.