Exactly! They study a set of genetic early risers. People with THOSE GENETICS have a lower risk of depression.
Forcing yourself to get up earlier was not studied. Not in any way!
And let’s face it, people genetically predisposed to sleep later are more likely to be getting forced by life to wake up before their genes want to (try being a sleeps til noon person in a 9-5 world). Which is probably going to do bad things for their emotional stability.