If there were known coordinates, why do whatever they did to color the target?
Two reasons: 1 - They were testing optical detection/tracking, either in the weapon or another platform (satellite?). 2 - They wanted to show off.
(On the other hand they might have painted the rectangle around the craters, a technique acquired by their cyber-espionage campaign against the US defense industry.)
It would be nice to have the original Google Earth image. Then we'd know if the Argentine guy was right about the size matching the centroid of a US carrier.