Is it just me struggling to make sense of that?
No, but I think he means he was asked to be below 700' AMSL (500' AGL, 200 FE) at 9 miles.
Firstly there is only one military airfield that has its own CTR - all others have MATZ and as ShyTorque states at 9 miles you'd be outside (laterally) or under the stub.
The word "Unable" is seldom used by PPL for fear of being denied a clearance (in this instance no clearance is necessary anyway). Remember, the MATZ is not controlled airspace and therefore you can be 'firmer' with your response and state that you will be maintaining X altitude or Y height and whilst we all want to be helpful THEY CANNOT INSIST you obey their instructions. You must, however, respect the ATZ which is usually 2.5miles away from the centre of the longest runway. Perhaps a sharper controller would have vectored you away from the main runway/circuit to enable more 'vertical distance' between you and the ground.
Without wishing to be disrespectful, I find some controllers issue instructions so they don't have to do as much/any controlling.