Lots of discussion about your heat gun and it's possibilities, how to measure temperature with your fingers and "I do it this way" posts. But I think this, the quote above, is the problem. What is your source of info? Was the source an article in a gun magazine, or on a forum?but I came across some information stating that a few seconds at 800* will anneal a case.
You reloaded and shot the brass with no problems. No loose bullets from too soft brass? No weak crimps from too soft brass? I wouldn't worry...