You're quoting out of context. The full quote: "For compatibility with operating systems that do not support this function, call GetProcAddress to detect whether IsWow64Process is implemented in Kernel32.dll. If GetProcAddress succeeds, it is safe to call this function. Otherwise, WOW64 is not present. Note that this technique is not a reliable way to detect whether the operating system is a 64-bit version of Windows because the Kernel32.dll in current versions of 32-bit Windows also contains this function".
IOW, just checking for presence of IsWow64Process() function in the Kernel32.dll is not reliable way to detect 64-bit OS. OTOH, using the IsWow64Process() in 32-bit application to detect 64-bit OS is fine.