This match was not important for New Zealand. Because New Zealand team had won the first two matches of the series. New Zealand had already won the series. So I think New Zealand players did not give full effort in this match.
However, Sri Lankan batsmen played very well in this match. If Sri Lankan batsmen could have batted decently in the last two matches, then maybe Sri Lanka would not have lost the series. In the first match, Sri Lanka gave a target of only 179 runs. And in the second innings, Sri Lanka had collected only 142 runs.
That is fair way to look at match. Because New Zealand had already won the series they probably did not try their hardest. But Sri Lanka batsmen played well in this match which makes you think about what could have happened if they had played like that in other matches. First match was especially missed chance for Sri Lanka because they did not score enough runs. If they had batted more carefully in that match result of series might have been different. By the way this match was amazing and I congratulate Srilanka on their win.