The Ken Thompson thing is presumably in reference to his popular piece "Reflections on Trusting Trust" (https://www.ece.cmu.edu/~ganger/712.fall02/papers/p761-thomp...)

As the level of program gets lower, these bugs will be harder and harder to detect. A well installed microcode bug will be almost impossible to detect.

And this is even lower - in the hardware itself.

Really fascinating work.