BMI doesn't mean much without knowing a persons fat percentage.
Based on direct and recent personal experience ... BMI means enough to be used as a qualifying criteria for some surgeries.
The relationship between BMI and % body fat is tight for example this study
Maybe for Sri Lanka with a uniform ethnic and socio-economic demographic... but not so sure for New Zealand with a more diverse ethnic and socio-economic makeup.
I, am surprised for surgery that they'd bother with it given there would be various physical examinations and tests before the surgery anyway that are more accurate.
BMI is a pretty rough measure. Any mesomorph or athlete with muscle mass will most likely come out as overweight.