I'm surprised that nobody has mentioned the possibility of the unknown transmission coming from some unauthorised person with a handheld transceiver?
I'm not; that's in the realms of conspiracy fantasy. Who would such a person be, why would he identify himself as "Airport Command RF 2", what would his motives be in saying "Airport Command RF 2 I'm telling you not to evacuate yet".
Please don't try to persuade us that a manager from the airline just happened to be hovering around airside watching the incident unfold, just happened to have a handheld on the right frequency, and decided to call himself Airport Command RF2 so that he could prevent an evacuation and save a bit of money at the possible expense of passenger and crew lives.
And if your theory is that someone else did it, who? why? etc etc.
It was someone from the RFFS, probably the Duty Commander or equivalent, aka Fire Chief, and my guess is that he said it just before getting off the truck at the scene, hence the words "he's on the ground" or whatever it was. From what he could see he probably thought it was justified, but he should not have framed it as an instruction which he was powerless to give, he should have offered it as advice, WITH REASONS. The word "yet" may have meant "I'm taking a closer look, hang on". None of which justifies the way it was done, but may well explain it.