Two questions:
How do you know it was a 747? The reason I ask is if it was close enough to identify, ATC would not let it 'dump fuel'!
How did you gather it was Japan Airlines?
Actioning the 'Fuel Jettison Checklist' is only done when the aircraft is above the Maximum Landing Weight and a landing is required as a matter of urgency. Under emergency conditions, the aircraft can be landed above Maximum Landing Weight.
No dramas in the news tonight!
Interesting none the less.