In which case, said guy is:
- not suffering Androgenetic Alopecia, or;
- is allergic to dutasteride and this is manifesting as Telogen Effluvium, or;
- the dutasteride is fake or;
- is unable to metabolise dutasteride for some very weird reason, or;
- is on a steriod that mimics DHT.
dutasteride annihilates 5ar. 5ar is the only mechanism by which DHT is made in the body unless you're shooting up a steriod like 1-test which will convert to DHT regardless (and no-one really knows how yet). So no or negligible 5ar = no or negligible DHT = drastically less receptor binding (test has a much lower affinity for the receptor than DHT) = drastically less hair loss.
Unless, of course, one of the conditions in the list applies.