No, of course they didn't:
"Using a child's body mass index (BMI) as a measure of the success of exercise targets may be misleading, say experts.I've always been a tad sceptical about the old BMI as an indicator of health for a couple of reasons:
UK researchers could find no difference in BMI between those exercising regularly and those missing targets.
Writing in the Archives of Disease in Childhood, they said blood testing might be the only way to measure exercise benefits.
However, another scientist said BMI did offer useful information, and testing should continue."
1) I appreciate it's very unscientific but I've just always had this sense that the whole measure expects people to be unreasonably light. I remember when I got divorced and lost a shit load of weight. According to the BMI, I sat comfortably within the range of being my ideal weight. But I looked like a heroin addict. People were worried about me and insisted I eat more pies.
2) Your average heroin addict probably has an excellent BMI ratio.