I'm just curious how far the neighbor was from your house while he mowed?
We live in a pretty rural area, and at night you'll get some of the neighbors hound dogs barking all night long along with some other's roosters going at all times in the morning, to the point where if your window is open, either night or morning, if you're a light sleeper, your sleep may be disturbed a little.
Ultimately I can't figure people who cut their lawn so early anyways. Not the best cutting time. Considering the guy is retired, I'm guessing he didn't have some time constraints to get it done. I will note that sometimes during the summer months I'll break out the chain saw around 7 in the morning just to beat the heat by 11, but if I'm cutting around a neighbors house (about 50 yards away), I'll usually wait till 9.