Orbital habitats are spacecraft. There's a pretty obvious and big mechanical difference.
But that doesn't actually matter.
The game does not model the commute of workers or the cost of transporting goods so it's meaningless whether population commutes from orbit to the surface or across oceans or is actually housed entirely in an underground bunkers - that's all left to the player to describe/imagine how they see fit for their "story". Neither does a TN-nuke care whether it's target is an orbital habitat, destruction of which might turn population growth negative, or the population itself - both cause a loss of population, one just does it more rapidly than the other.
I was suggesting urbanization tech due to the following reason: A lower tech level society cannot support the same number of people on a planet as a higher tech one, I am proposing to model that.
Unless I'm misunderstanding what you mean here, this is still completely irrelevant. We're not talking about Medieval urban areas without sanitation, health services or refrigerated food transport. Once you have running water and electricity and vaccinations, there is technically no limit to population density that your society can support.
And because Aurora does not model any of that, adding a tech line that arbitrarily increases population density seems pointless. There already is a Construction tech line that makes Infrastructure more efficient and a Biology tech line that makes Terraforming faster.
I'm sorry if I come across as hostile, that's not my intention. Again, if/when Aurora models civilian society down to food, energy and health care production/consumption/distribution level, then your proposal would absolutely be useful and should be added.