I would have guessed, even before reading those sites (and thanks for sending) that middle-income was where you'd see a higher incidence in weight.
Having worked in WIC and having been in every health clinic in Georgia in the early 1990's, I definitely "get" the notion of the perceived connection of obesity and lower economic status. But I also think much of that is based on individual observations.
Again, it all comes down to personal responsibility. I think BMI is directionally more valid than invalid. Mine was as high as 31 in early 2017 - way too freaking high. It's about 23.2 now.
Yes, I was accused again yesterday of communicating a message of shaming, simply because I said the following: "It could not possibly have been good on my organs to carry around that much weight"