The author is confusing two completely different things and comes to a wrong conclusion.
He states that C isn’t low level because CPU are much more complex today. But those aren’t related. His argument would be no different if he claimed assembly isn’t a low level language.
That the CPU speculatively executes instructions and maintains many levels of cache doesn’t change that C is low level. Even if you wrote a program in OP codes you can’t change that.
There was a single paragraph to support his argument that was optimizing compilers can create machine code wildly different than what might be expected.
Then he goes off on a complete tangent of how C isn’t good for parallel processing which has nothing to do with his thesis.