I agree. By the time you pick yourself up from the ground the horse doesn't necessarily connect anything with the buck. However, by being nice to him you are encouraging him to stay with you if/when you fall off. In this case you were very quick to be at his head, but still, the time to deal with a buck is when you are on top, not on the ground LOL
And, ya, everyone call tell you what to do in a buck, but since you weren't paying attention, it doesn't sound like you would have had the chance on this occasion. If you have the opportunity, yes circles will limit the buck because it will throw him off balance. Keep your weight back and low.