[kirubakaran]

What you experienced is a "near miss" and it probably happened only because someone somewhere fucked up.

http://en.wikipedia.org/wiki/Near_miss_(safety)

[mikeash]

In my opinion, it's far more likely that he greatly underestimated the distances between the two planes. People who aren't used to these things tend to see a few miles of separation as a few hundred feet instead. Airliners are big.

[sukuriant]

This is an incredible possibility.