He's assuming infinite elasticity, which isn't how prices work in real life.

The typical version of this argument is that the people who are being taxed in the first place are the ones increasing rents. In which case taxes can then be increased until the desired equilibrium is achieved.

That's not to say we couldn't also provide a basic safety net like he describes. But that raises the question of why UBI should stop there. If our economy can generate a surplus, then why shouldn't all humans sharing their slice of the Earth get it?