It's clearly not full auto or burst fire. Urban rifle training in the military teaches 2 rapid shots center mass to the target. If it doesn't drop, take 1 well aimed shot at the head. If there's multiple targets, put 2 rapid shots center mass into each before aiming for the head.
He's firing two rapid shots, changing targets, two rapid shots, changing targets, and so on... There's occasionally a 3rd shot. As an instructor, he was teaching people how to do this all the time, and probably 90% of his live fire training was spent putting 2 shots into everything.
I'd also guarantee while he's inside with an optic, he's using a shooting technique where you keep both eyes open, and your brain projects the reticle on the center of your vision while maintaining reasonable accuracy. It allows you to take those 2 quick shots and quickly change targets.