READ the spaceship book aloud, show the kid the pictures of the moon and Tranquility Base and before you know it, she's reading them to you. No boring primers necessary. That element definitely exists in unschooling, but I'm not sure that's a basic tenet. I don't do unstructured homeschooling or relaxed homeschooling. Alex, on the other hand, has never had a lesson from me that he didn't request and initiate.
Labels exist to stop discussion.
Give it a name, put it in a category, and you've captured it and made yourself safe from it. Unschooling scares people, because there are no guarantees. How it appears in different homes is as individual as the child himself. In some cases, unschooling parents will find their child desires a structured curriculum, and they provide it. The difference is in WHO is asking for the curriculum, and who is responsible for doing it.