I dont think C was ever a low level language in the sense "close To cpu", or maybe very long time ago.
On 286, memory was segmented, and C compilers wrapped the whole program To a single segment, IIRC, you could never manipulate segment register directly in C.
Then 386, added paged memory, multi tasking, etc, you couldnt touch that with C.
Then pentium with pipelines etc, then mmx, simd, still nothing To manipulate this in C.
But if low level is taken as in "low abstraction level" then its more true, and it means C program are built with very simple abstraction that allow to define every small step of the program, without any "implicit logic".
RE: C is not a low-level programming language