Firstly, I hope the poor chap makes a speedy recovery.
About 29 years ago I did a gliding course at Sealand. I may have convinced myself of this having mulled this over on more than one evening but....
Doesn't the disturbed airflow as a result of the brakes being open make a dramatic contrast in wind noise? I'm sure I recall it making a din.
If this is the case, wouldn't a pilot recognise this sound?
As I said, it was a long long time ago now.