Its another one of those misaligned bits of rule making that crept in rather than being intentional I think. I don't that EASA even grasped the concept that people may be Ground Examiners without being flight examiners as well!!
Generally speaking the Head of Training will be a Flight Examiner as the have to demonstrate a certian level of experience in order to be accepted by EASA to fill the role. Invariably in gaining that experience we became flight Examiners on the road!!