I only skimmed the text, but wonder if this study had controls for their social lives and mental health. These behaviors are also on their own indicative of depression, because it often interferes with sleep patterns. It becomes a causation/correlation issue?
The article states: “They also tested the possibility that it was poor mental health causing people to stay up late, not the other way around. They tracked a subset of participants who had no previous diagnosis of a mental disorder for the next eight years. During that time, night owls who slept late were the most likely to develop a mental health disorder.”
A diagnosis requires crossing a certain threshold of suffering to even get diagnosed, also stigma is a reason many people still refrain from seeking diagnosis. the night owls might just not yet have been diagnosed at the time of this study
