In the list of intentional homicides Sri Lanka indeed ranks higher than I expected, rank 132 of 230: https://en.wikipedia.org/wiki/List_of_countries_by_intention...
About being calm: I agree about the anger on roads. Except for that my impression was a calm and peaceful one -- maybe what you encounter as violent is still OK from my culturally distinct perspective? Do you think there are many 'fights'/arguments where people are shouting in the public, or would such a thing happen at home?
And what is your opinion about the high suicide rate?