This is interesting. Personally I did not need to "encounter" async. At some point I realized that I needed it in my project (it did not have that official name back then) and had written an implementation in a few days. I also written preemptive multithreading library in ancient DOS based product with having zero prior experience. Again took me few days.
Seems totally normal. And most likely, after a few weeks this person would get the concept.