Agreed -- if it were a 737 and 747 maybe, but an A300 is a small widebody, and a 777 is only a mid-large widebody. They aren't _that_ far apart in size.

I guess if it was a really, really long lens, such that one plane is 20,000 feet away and the other is 21,000 feet, you could have them appear at relatively the same distance, yet still have the requisite 1000 feet of vertical separation.

The British air traffic authorities said something about the especially blue sky that day contributing to the optical illusion, no doubt with an extra contribution from swamp gas refracting the planet Venus.