I still agree that he is dangerously ambiguous and mostly incorrect though.
But there's an entirely different class of mental illness that's closely tied to depression; those caused by chemical imbalances in the brain. Stress often amplifies the symptoms (think of people with multiple personality disorder, schizophrenia, etc) but isn't the root cause.
I imagine the founder you're quoting has never had a close friend or family member that suffers from the latter. I get that they might not understand but it's unfortunate they hit "depression" with a sledge hammer by generalizing it so much.
I would imagine the same, except for the description s/he gives for depression where s/he describes it as being a numbness that can be addictive to fall back into. It is such a spot-on description that he either read it someplace or went through it personally.
That being said I agree that drawing a line is difficult and possibly counter productive. When dealing with people's lives it can lead to more confusion than it helps explain.
