The "military radar" being referred to here is not an ATC radar but rather the type of radar designed to detect uncooperative aircraft such as an enemy which is not squawking any kind of transponder. One part of such a radar is that which tries to verify an aircraft's altitude by triangulation of the direct range and the antenna elevation angle: there are potentially large deductive errors if such a radar has not been "calibrated".
It's no surprise to me that such a conclusion might be reached.
