What does exposure before mastery actually mean?

It means the goal is recognition, not competence.

Your child does not need to retain these explanations, repeat them back correctly, or be able to use them. There is no test and no correct sequence.

What we are aiming at is one quiet moment years from now when a familiar word turns up in an unfamiliar room and does not feel like a wall. A child who colored a lemonade stand at five is not doing marketing. They have a hook for the real version later, which is a modest thing and enough.