Really short: ECS existed in the earliest implementations of OOP in 1963 and was being used in the software he showed.

When OOP went mainstream it pretty much was entirely about "compile time hierarchy of encapsulation that matches the domain model" and nothing else. His opinion is the standard way of doing OOP is a bad match for lots of software problems but became the one-size-fits-all solution as a result of ignorance.

Also he claims that history is being rewritten to some extent to say this wasn't the case and there was never a heavy emphasis on doing things that way.