He's not wrong. Windows Server 2008 R2 is based on the 64-bit version of Windows 7, not on Windows Vista with a service pack, unlike Windows Server 2008 was based on Windows Vista with Service Pack 1. If you call Windows 7 a revised version or release 2 of Windows Vista, not Windows 7, Windows Server 2008 "R"2 is a revised one or release 2 of Windows Server 2008. If not, Windows Server 2008 "R"2 is NOT a release 2 of Windows Server 2008, but a new Windows server, "Windows 7 Server".
Microsoft class Vista to Windows 7 as a major update, yet they class Server 2008 to Server 2008 R2 as a minor update. Seems abit strange if its the same code. But lets not forget Vista SP2. Which again they class as a minor update when moving from Vista or VistaSP1