Why Does the NetBSD System Call Manual Mention the Standard C Library?

I'm reviewing man(2) pages on NetBSD 9, and have seen that all of the documents (write(2), open(2), pipe(2)) mention the Standard C Library at the top. My understanding was that system calls were independent of library functions (such as those in libc). I don't see a similar mention in the Linux System call Manual. Does this mean that invoking these methods is calling some wrapper function included in libc, instead of directly calling a kernel function? Is this generally true, or just a feature of NetBSD?