I don't know...
Judging from the size of the two planes (an A300 is about 177 feet long, a 777 about 209 feet long), and that the smaller of the two planes actually appears to be closer, I'd say those planes were pretty damn close together. In a quick test I ran of 3D models of the two planes, if the A300 was a thousand feet in front of the 777, it would appear to be almost exactly the same length as the plane beyond it. It would help if I knew the exact lens he was using.