Nope. "Urbanist advocates" can create real estate bubbles even with a shrinking population.
Case in point: Tokyo. You just need to make sure you _have_ to live in The City, and that there are no other options for you. And a shrinking population makes that _easier_.
Case in point: Tokyo. You just need to make sure you _have_ to live in The City, and that there are no other options for you. And a shrinking population makes that _easier_.