If Thomas Friedman's column in the New York Times was correct, the Chinese pilot was merely holding up a sign with his own, personal e-mail address.
What did this "mean"? I don't know- in "Top Gun," what did it mean when Tom Cruise's character flew to within 2 feet of a Soviet MIG and took a few Polaroid snapshots?
All it meant was that fighter pilots in EVERY air force around the world tend to be hot shots, showoffs and wise guys, with a strong childish streak. And they tend to treat peacetime encounters with "the enemy" as a game.
Bear in mind, the Chinese pilot had been sent up to harrass (but not attack) the American spy planes many times before.
He was probably USED to seeing that plane, and the American surveillance team was probably used to seeing him. And while they certainly never got to be friends, there may well have been a certain amount of good-natured mockery and teasing on both sides, for some time before the fatal accident.