Not the entire genome, if that’s what you’re referring to. Just the y chromosome. He created a family tree using his mutation rate for the y chromosome and counted the branches to get population over time and matched that against historical data. It’s covered in this video. I don’t understand entirely if the rest of the genome and the y chromosome can have different mutation rates or what but it would be very weird for him to claim to be able to make testable predictions about history that we haven’t yet uncovered when it’s just bad science.