I strongly believe it is indicating that the 'Unknown' person transmitting, not identifying themself, is telling 'Airport Command RF' to not evacuate yet,
Nope, I don't buy that.
If an unknown person wanted to give a "command" not to evacuate, he would address that "command" to the Captain, not to someone in a fire truck. Telling 'Airport Command RF2' not to evacuate makes no sense whatsoever.
In any event, the conspiracy theory of some senior company person suddenly appearing on the airfield as this emergency took place, and then acquiring a radio on the airport's ground operations frequency, and using it to issue anonymous orders to the aircraft Captain just doesn't stack up.
My money's on a Fire Chief with a misunderstanding of his responsibilities and authority, which is not to say that he is not totally competent otherwise.