Well, he built a model that behaves this way. Whether that model is correct or not is another question, but the author should at least give insight as to what exactly in that model doesn't hold. The negative impact of social housing is an outcome of that model, as far as I understand.

Note: I'm pro social housing as I have anecdotal evidence for how well it works, however that's in a completely different system than the US, where urban planning puts high importance on mixing up low-, medium- and even high income areas to create opportunities for social mobility.