He has a point – which is that with remote work proving feasible and high salary expectations on the coasts, a lot of companies will be looking for talent elsewhere – either in the middle of the country, or on the same timezones outside of the country.
He's not saying much though, because salary / benefits expectations and what a company is willing to offer are all part of the free market dance, which takes some time before it reaches a "final" state.
A company that will reduce salaries tomorrow will find itself in a difficult position – difficult to find new people, maybe bad publicity etc. But over time (years, a decade?), salaries will likely normalize due to companies hiring cheaper developers piecemeal.
Not all tech jobs are equal, and while some engineers will always be able to charge a premium, others won't. Similarly with good managers, PMs etc.