He specifically said he had another "mental" diagnosis. Therefore there's no reason to start speculating about a neurological cause.
My own depression could very likely be neurological because the co-morbidity of psychiatric depression with seizures is extremely high, around 50%. Regardless, Cognitive Therapy turned out to be an extremely effective way for me to manage it.
Believe me, I read what you wrote carefully:
This clearly associates all non-situational depression with a neurological problem. In fact, though, the bulk of people being prescribed meds by psychiatrists for depression are not considered to have a neurological problem.
The effectiveness of Cognitive Therapy is independent of the cause of the depression. That's one of it's distinguishing features: it targets the here and now manifestations, not the causes.