Maybe some forms of depressions are, but certainly not all of them. Sometimes circumstances are actually depressing, and people become depressed as a result.
Sure, the actual depression is something physiological (neurons firing, hormones, whatever). That doesn't imply that it is caused by physiological malfunctioning.
The article refers to some form of clinical depression. Having the blues is not depression. Although we dont know the exact correlates of depression, we know it has something to do with neurotransmitters and is most definately physiological (note how hormonal changes such as birth can cause depression, or how SSRIs are used to treat depression). It's the denial of this fact that usually leads to drug aversion.
Sure, the actual depression is something physiological (neurons firing, hormones, whatever). That doesn't imply that it is caused by physiological malfunctioning.