>>10A C compiler could be non-portable, but C as language will be portable.
The C language is far less portable than traditional high-level languages like Fortran, Algol, and Basic. These languages can run better on tagged architectures and high-level computers. C can't compile to more advanced hardware, so people stopped building it. If you're wondering why OSes have separate address spaces and no orthogonal persistence, it's because we use C.
The real point in what he said is in a way is even more powerful: C was/is good enough that basically every processor these days is a “C machine” — byte addressable, 8 bit bytes, sizeof (char *) == sizeof (int *) etc. Anybody who started programming after the early 80s probably can’t imagine programming anything else. Essentially, C fit _a lot_ of the hardware (basically, IBM-style hardware, though it was developed for the PDP-11) so people stopped building hardware that didn’t look like a PDP-11. A virtuous network effect.