I don't believe that the statement about sugar metabolism in Asians is true either but I would love to see a reference to support such a statement. Always ready to learn.
It is true that for some Asian populations that the risk of diabetes appears to increase at a lower BMI compared to other populations, so it probably is appropriate to use different BMI standards for adults to define obesity/overweight (not that the thresholds we are using of 25 or 30 kg/m2 respectively are ideal in terms of defining risk).