Abrupt change in toddler behavior

I've been battling with the "terrible twos" attitude my son has had for a very long time now, and finally I am seeing light at the end of the tunnel. It seems like all of a sudden his attitude is much better on a daily basis overall. He wakes up with smiles instead of screams and when you ask him a question he answers nicely instead of always saying "NO".

Mealtimes have been a lot less stressful lately too, which is directly related to the little one's behavior. We used to have a full four hours a day of whiny, pouty sounds from him, and now that has completely stopped. The weird thing is, I've been trying to figure out what has changed in our lives and really there is nothing. If anything, the kids have been going to bed later than usual since it doesn't get dark until after 8:00pm. But you can't tell me less sleep would improve a kid's behavior, could it??? Regardless, I am very glad this phase is passing and happy to see my son's smile regularly again.