There is big difference here between portable ISO C vs C with compiler extensions and platform specifics.
I don't think anything here is in conflict with the statement that Fortran can be faster than C in some cases, but yes you're right that technically that should be qualified as naive Fortran can be faster than naive C
You can inline assembly in a lot of languages. However I’d argue that doing so is thus no longer writing code in that host language.
To put it another way, your comment is a little like saying Bash is just as fast as C because you can write shell scripts that inline assembled executables.
Fortran just has better syntax and defaults than C for this stuff. A devoted, expert C tuner with unlimited time on their hands can do anything. A grad student with like a year of experience can write a Fortran code that is almost as good, and finish their thesis. Or, a numerics expert can write a numerical code for their experiments and be reasonably sure that they are operating within a good approximation of the actual capabilities of their machine (if you are an expert on numerical computing and C+assembly, you can write a library like BLIS or gotoBLAS and become famous, but you have to be better than everybody else in two pretty hard fields).
IMO this is important to point out because somebody can bring a microbenchmark toy problem to show C beating Fortran easily. As long as they spend way more effort on the problem than it deserves.