I suppose that depends on when the home was built/receptacle was installed. If it was originally a 2-wire receptacle back in the days when that was allowed, and it was later replaced with a GFCI receptacle, then it's fine as long as it's labeled "No Equipment Ground" (406.3(D)(3)(b)). On the other hand, if a ground was required when it was installed, and the installer omitted it anyway, then it's a violation.
In my (admittedly limited) experience, Home Inspectors have a checklist of things they look for, and that's it. Their lists tend to include the general rules and ignore the exceptions, because (1) it's not realistic to expect them to memorize the Electrical, Mechanical, Plumbing, Building, and Energy Codes; and (2) they're looking for things a prospective homeowner might want to know going in, not necessarily Code violations. He probably plugged in his tester, saw the "No Ground" LED light up, and marked it down on his form, without knowing or needing to know if it's really a problem or not.