C symbols are supposed to be in std if you use the cstdio style headers. It’s just that for a very long time compilers put them into the global namespace too.
In fact, the last time I checked, the MSVC cstdio header was implemented more or less like this:
namespace std {
#include <stdio.h>
}
using namespace std;
I had absolutely no idea this wasn't even supposed to be the case (although I was aware of the duplication in std::). Guess it makes sense that the standard would shy away from global namespace pollution - I suppose one of the compilers perhaps did this for long enough that the others ended up duplicating it to increase code compatibility?