Two Freqs
One of the problems at many US airfields-certainly JFK and LAX-is that the ramp is 'owned' by (usually) a company with it's own freq whereas the taxiways are controlled by the ATC tower. This has probably provided the conflict in this instance. The commuter had signed off from the freq that the A380 was on and probably had no knwoledge that the A380 was bearing down on him.
This happens nowhere else in the world so talk of 'busiest airfield' is wide of the mark. At LHR even though the ground control is sometimes split at busy times into North and South (as at LAX) the controller looks after the a/c until it's parked, not until it's about to go into the ramp area.