As stated, you'd need to purchase the expensive land and then turn it into housing. This is done in Los Angeles, but the property that is built isn't cheap affordable housing.

He didn't say it would be cheap affordable housing. He said it "will relieve price pressure on existing, overpriced older housing". Which makes sense. Normally new buildings are the luxury housing and over time, as they become outdated, they become the affordable housing. Building new "affordable housing" is a fools errand, since it costs almost as much to build as luxury housing. You just build more housing period and let nature take its course over the decades.

Yep. And don’t we have to wait for the new expensive housing to trickle down and become cheap. If enough new housing is built, the older housing becomes cheaper almost immediately.