I'd heard their relative advancement put down to the fact that they have land that is replenished by the river every year with the result that they never exhausted the land, which was a problem for other cultures until they learned about crop rotation and fertilizer. Note the very strong links between Pharaonic ritual and the annual flooding of the Nile.From everything i know of the Ancient Egyptians..... I have always believed they had were ahead of their time. Even to this day, more and more is being un-earthed about them. It was a huge shame the civilisation died out as i wonder how advanced they would have been in the 21st century??
This meant that the Egyptians had a more reliable food source than other contemporary cultures ( though I'm not sure what China was up to at the same sort of time).
Then you add the fact that round this VERY fertile strip of land there was - even back then - a lot of desert that was difficult to get across, especially with an army. This gave them security from outside intervention.
Add a reliable and abundant food source to security from outside threats and you have a very good cradle for civilisation, and one not available to other cultures that I know of, with the possible exception of China. We do not need to turn to aliens to explain it.