I feel like, what is confusing you is that the parent is talking using broader/more general terms, rather than about specifics i.e. the state as an object which

I feel like, what is confusing you is that the parent is talking using broader/more general terms, rather than about specifics i.e. the state as an object which you can pass inside functions. His point, I believe, is that what causes problems/bugs is often when partially invalid state is shared, not so much specific implementation details like "are the modifications to the state visible because of mutation or because a copy of the state is passed around explicitly".