The key part is that it's related to the circadian rhythm and time keeping. That it's persistent and recurrent doesn't in itself distinguish it from other sleep disorders that may cause delayed sleep schedule, such as sleep-onset insomnia, or "bad habits" as you call it.
> Adding a distinction could help. Perhaps "voluntary night owl" vs "involuntary night owl".
If you want to address people affected by e.g. DSPD, and not "night owls" in general, it is perhaps just better to simply address them as such.
That certainly fits the description of "night owl," but I don't think there's anything clinical about it. My particular manifestation is more of a lifestyle choice, and based on what I observe in the tech field I'm hardly alone in making this choice. Folks who do have a sleeping disorder causing night owl tendencies to manifest (especially when they'd prefer, socially, to rise early) are in a different boat altogether, and I'm... honestly not qualified to classify them. It's an interesting space.
"Circadian rhythm sleep disorders are characterized by a persistent or recurrent pattern of sleep disturbance (difficulty falling asleep or staying asleep and excessive sleepiness) due to alterations of the circadian timekeeping system and/or misalignment of the endogenous circadian rhythm and the external environment." https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3523094/
Key part of this being "persistent or recurrent". In other words, people who have been struggling with this for a long time and have it reoccur after trying out different strategies.
Adding a distinction could help. Perhaps "voluntary night owl" vs "involuntary night owl".