It must have been unusual enough for him to take the photos. If you look at the link in Eno's topic on this subject there's a series of shots. I think the relative size of the two aircraft adds to the illusion. The wingspan of the A300 is considerably smaller than the B777 above it.
To the naked eye, the effect may have been similar... I've often taken note of planes crossing overhead; it grabs your attention sometimes. But it's usually easy to tell they're properly spaced.
BTW, if anyone cares- I see I misread igs942's post... he said "under" FL290, not "at".... there; i feel better now.

Some people really ought to just mind their own damn business...
