Depression is not (yet) characterized by any physical cause. The only definition of clinical depression is a set of behavioral symptoms. If he didn't have those symptoms (even in retrospect), then he wasn't depressed. "The diagnosis of major depressive disorder is based on the patient's self-reported experiences, behavior reported by relatives or friends, and a mental status examination." https://en.wikipedia.org/wiki/Clinical_depression
Sure, but you will never find a clinician who would base their depression diagnosis based only on behavior reported by a significant other. Especially immediately following a suicide.
