It is possible to place the clamp at the wrong height on the distributor which will cause the distributor gear to barely engage with the camshaft gear. Once you drive it this way, force exhibited by the camshaft can force the the distributor up slightly, disengaging the gears from each other allowing it to jump out of time.
This happened to me one time. I was as lucky as you. No harm done except pride. On a side note, the the end of the distributor shaft remained engaged with the oil pump the entire time prior to the jumping of timing.
