What technology? The main technology needed to work gold leaf is a smelter to pour the initial shape, and after that you don't need any weird materials or machines, it is just skilled and careful hammering. Going thinner doesn't require a different technology, it requires a more skilled goldbeater, even noways sub-µm gold leaf is routinely done with traditional methods.
Why do think they weren't able to get it that thin? What "technology" are you referring to? Here's Wikipedia's summary:
"5,000 years ago, Egyptian artisans recognized the extraordinary durability and malleability of gold and became the first goldbeaters and gilders. They pounded gold using a round stone to create the thinnest leaf possible. Except for the introduction of a cast-iron hammer and a few other innovations, the tools and techniques have remained virtually unchanged for thousands of years."