Recall practice IS learning. Projects, exploration, and discovery-based "learning" sounds great in theory but in practice, without actual testing, really doesn't live up to the hype.
Adam Boxer is worth reading.
If you're flailing around without having memorized basic trigonometric identities, you're going to struggle severely to apply them to classical mechanics. If you can't do basic matrix multiplication, you're not going to build a graphics engine.
The article tries to damn Khan with an example about probing how neural myelination works. If you understand the foundations of electricity (by learning about capacitance and impedance) and have done some grueling foundational learning in organic chemistry, ready answers might spring to your mind. You need the former to make asking the latter fruitful or meaningful.
Khan deliberately uses the term "scaffolding" - which since we're throwing around dead education theorists harks from Vygotsky - which is precisely what a teacher provides by pantomiming elementary concepts for a child. Ultimately the child needs to internalize these basics to succeed in more complex projects with a sense of independence.
I really don't understand this article. Two things can be true at once.