Well, that's just plain ridiculous. Your 'perl -V' quite explicitly states that "$Config{'archname'}-$Config{'osvers'}" is "MSWin32-x86-multi-thread-5.0". (Look for 'archname' and 'osvers' in the output.)
I guess there's a rational explanation - though I really don't know what it is. How can 'perl -V' claim that 'osvers' is 5.0, but $Config{osvers} report 4.0 ? Someone has stuffed up something.