Thanks Titan. In the report, the CAD seemed to agree with the downgrade because, if FULL EMERGENCY is declared, firefighting equipment is deployed from outside the airfield (which I thought was a good idea). This aircraft stopped 390M from the end of the runway so one more bounce, a few pounds less pressure on the ( manual) brakes etc etc and it would have been over the fence and in the Highway! Then all the firefighting assets in the area would've been required. As you say, who has the authority to downgrade a MAYDAY. It's either a MAYDAY or it isn't - or so I thought.
"Cathay 780 are you declaring a Full Mayday or just a normal one?"
Mindboggling!!