[Strilanc]

The article explains in substantive detail...

- How quadratic residues can factor a modulus.

- How to take a signal with peaks at k/P and derive P from a single sample.

- The general flow of modular-exponentiation to period-finding to quadratic residues to factoring.

But that's all mostly classical stuff that programmers would be expected to be able to follow in full detail. You're right that there is no focus on the fundamentals behind the QFT. Instead, there's a focus on concrete "if you do this, you get that" examples with links to a simulator to back up those assertions.

Some people learn best by starting with fundamentals. Others learn best by starting with examples. Most do a bit of both. It's inaccurate to call something "pop science" because it did some concrete-example-first explanation. Pop science articles don't have fundamentals or concrete examples. They just make joke analogies to Doctor Who or whatever and call it a day.