> The causes of my depression were environmental. I grew up in a very dysfunctional family in Minnesota. My parents were both alcoholics and depressed, and their dysfunction became my growth environment

This may be the case, and there may be corroborative evidence for such a conclusion that we are not told about.

But as presented, it's just a set of circumstances, presumably correlated. If both parents suffered depression, author might reasonably be supposed to have a strong genetic predisposition.