I'm Mexican, and this results baffles me too. I would say that maybe current perception of government corruption (which has been declining for years and is really really low) has a lot to do, since many people might feel that Mexican society is in debt with them because of the poor perception we have against the current state of affairs.
Also I wonder if this was done in big cities like Mexico City (my guess) or more evenly distributed. I have a perception that Mexican society in general is pretty honest, but big cities are more rootless and impersonal. But this didn't seem to apply to India or other high density countries.
Other reactions. I wasn't suprised to see the United States right in the middle. I was surprised that Canada wasn't further up. I was surprised that Russia was ahead of Canada.
And what makes Mexico so different than every other country?