You're arguing different things. You're using a plain English version of the definition of "affordable," beaner is trying to describe the real estate term of art "affordable housing."

https://en.wikipedia.org/wiki/Affordable_housing

It's like "accessibility". Several times (long ago) I've mistaken that for meaning "easy to access" and been disappointed to find it was useless. I still don't know what a "walkable neighborhood" is. Can't you walk just as easily in any neighborhood? When I read this article, I wasn't sure if affordable meant restricted to poor people, subsidized, or small (cheap) houses. I only learnt the answer from this thread. These words are only useful to the groups who already use them and impede understanding to outsiders.

I don't think there's anything pedantic about it. The term "affordable housing" implies that housing which isn't subsidized isn't affordable. But the vast majority of housing is bought, sold, and owned by regular people without subsidizing. The term is not accurate at all. The fraction of housing that is only available to a number of people in the single digits is so small as to not be worth considering. "All but 0.0001% of housing is affordable" would be pedantic; "all housing is affordable" is not.