Hyperextension is when the elbow is bent backwards beyond the normal range of motion.
When measuring it in relation to a bowling action the hyperextension creates a negative angle, so if Bumrah had an elbow extension or flex of 10 degrees and a hyperextension of 10 degrees it's not a 20 degree flex (which would take it beyond 15) it's 10 because the hyperextension is discounted.
In that pic I posted, that is not his elbow bending backwards In hyperextension at 35 degrees. His elbow is facing forwards, his biceps is facing up and his arm straightens in the same direction as the ball is released which IMO is a chuck.
Not to start this up again, because my mind is made up, but that's how I read the rule, that's how I understand what a hyperextension is, you know, when I didn't fact check before I doubled down.