Perhaps someone accidentally left the doors open on the Atom CPU which allowed them to run a disassembler.

"In mid-2020, our team managed to extract microcode for modern Atom processors that are based on the Goldmont microarchitecture. It became possible to do this on Atom Goldmont systems-on-chip (SoCs) due to an arbitrary code execution vulnerability in Intel CSME (Intel-SA-00086)."

Probably using something like that: https://github.com/xoreaxeaxeax/sandsifter

They have been reverse engineering Atom for over half a decade (possibly longer) now.