It'll be something to do with air pressure. I'm assuming you were quite high up a mountain? At sea level, water boils at 100.C but the higher up you go the lower the boiling point because air pressure is reduced. It works out something like 10.C reduction for every 1,000 feet I think.
What this means is that your water was probably boiling at about 80.C, so while the water would have boiled quicker than usual it would have taken longer for the egg to actually cook properly.
yes, its the altitude. water boils (turns to vapour)at a lower temp at altitude, so the "boiling" water is less hot than it would be if you were lower down so the eggs take longer to boil.