I had to re-read the exception to 210.25(C)5 and the second sentence is pretty clear. Under the exception, for an outlet to be counted as as meeting 210.52(C) is has to be both not more than 12" below the counter edge and the counter can extend not more than 6". Sorry to say, but the inspector here is giving you a break by even measuring the outlet distance. The counter is too deep for the outlet to be counted under the exception.
I'm afraid I have to disagree, as to the measurement, with the more senior members of this board. The outlet is definitely 'below' the counter, no disagreement there. The code does not say 'directly below' or 'on a plane below' or 'vertically below' so the dimension can be measured on any applicable vector and the vector that is in question here is from the near edge of the counter to the outlet. An under-counter outlet is does not count as meeting 210.52(C) unless complying with the exception and to avoid omission should be unambiguously within the exception's 12" rule and this outlet is not. One should not be able to place the outlet any arbitrary distance behind the counter ledge and still argue "It's within 12 inches!"
In addition this outlet violates the spirit of the code section in that it would be impossible to safely place an appliance with a 12 inch cord on the counter and connect it to the outlet.