I agree with what some others have said or hinted at, particularly Redz. Smart has the body to avoid the physical beating that thinner players would take, but his style is so aggressive, I'd expect him to consistently play around 65-70 games a season. I don't think that's a terrible thing, especially if the alternative is asking him to tone down the aggression.
In addition, as KeepRondo said, part of this could have to do with Smart's confidence. Part of it also could have to do with the fact that it was a late November game against an absolutely awful team. If this is a crucial game in March vs. Atlanta, for example, and Smart's adrenaline is running high as he's having a good shooting night (7-12, or something like that), I wonder if he stays in the game.