Canada

Well first off that paper is from 2025, but data collection for the OP study is as far back as 2009.

second this is the first line of the paper you indirectly linked:

current BMI-based measures of obesity can both underestimate and overestimate adiposity and provide inadequate information about health at the individual level, which undermines medically-sound approaches to health care and policy."

This study is not information at the individual level.

And here is a quote from later on in the abstract:

We recommend that BMI should be used only as a surrogate measure of health risk at a population level, for epidemiological studies, or for screening purposes, rather than as an individual measure of health.

E: OP's study actually cites the new obesity definition in it's methods to justify it's use of BMI:

Not all individuals with a BMI of 30 or higher will have impaired health or increased risk of death, and some individuals with a BMI below 30 may also have obesity.18 However, for population-level screening and surveillance, the use of BMI categories as a proxy for obesity in adults continues to be recommended.9,14

citation 14 is that study referenced in Scientific American!