It's entirely plausible that some people have hereditary character traits that make them less resilient to stress. They're not necessarily depressed because of their genes, but their genes make them more vulnerable to depression.

We observe a similar phenomenon with diseases like type 2 diabetes. People of south Asian origin have significantly higher risk of developing type 2 diabetes, even after controlling for diet and lifestyle factors. We have identified a cluster of genes that don't directly cause diabetes, but seem to increase the risk of developing the disease. You aren't doomed to develop diabetes if you have these genes, but you do need to be more careful about your diet and lifestyle.

https://www.nature.com/articles/ng.921

The current mainstream view is that depression is partly physical, so you're not wrong.

(edited for clarity) Some say that depression is a chemical imbalance, but this is not a mainstream view any longer (I think, although it's often mentioned in comments on the Internet), although treatment is still very much based on chemicals like SSRI drugs, which have very little proven effect, require constant upping of dosages to gain the small effect they provide, and also having several undesirable side-effects.

I did not equate the two.

I did not say you did, sorry if it seemed that way, but others further up this tread are indeed saying that.