The strawman is taking “supply is an issue” to mean that “dwellings per capita is going down”. Or to assume that stating the former means stating the latter. Or to assume that the former implies the latter. Whatever framing you prefer.
If you disagree this is strawman, that’s fine. Maybe there’s a bette name and we can call it something else, sorry for the confusion. The main point is that “dwellings per capita is going down“ is not representative of the view that supply is a factor in housing affordability.
Even if he’s being technically correct, only a fool doesn’t understand the context and subtext of what he’s saying.
Even his dumb supporters get it.