How does he feel when he's that low?
It's possible that if he feels fine that he's just an individual who has lower blood glucose than the adverage person, but he be wise to speak to his GP about this as their is a diabetic condition when the body produces too much insulin, I know two people with this, my friend whose brother is T2, and my daughter friend whose does take tablets, and have to carry a hypo kit around with him... And I know his cousin is a T1 diabetic!
So he's best off talking to his GP about your findings..