Is 'bool' a basic datatype in C++?

Yes, bool is a built-in type.

WIN32 is C code, not C++, and C does not have a bool, so they provide their own typedef BOOL.

bool is a fundamental datatype in C++. Converting true to an integer type will yield 1, and converting false will yield 0 (4.5/4 and 4.7/4). In C, until C99, there was no bool datatype, and people did stuff like

enum bool {
    false, true
};

So did the Windows API. Starting with C99, we have _Bool as a basic data type. Including stdbool.h will typedef #define that to bool and provide the constants true and false. They didn't make bool a basic data-type (and thus a keyword) because of compatibility issues with existing code.