How? The UK has more anglo people than the US. Am I implying that Anglos aren't United Kingdomers or Americans? The US has more white people than Sudan. Does that imply white people aren't American?
It's logically implied by your words, "the US _seems_ like it is more obese." (Emphasis added.)
"Seems", as in "appears to be, but is not actually." The only way the US is not actually more obese is if Hispanics and Blacks do not count as "the US".
The only other way to read "seems" here is in the "I'm not totally sure, but this is what it looks like" sense. But this doesn't seem to be the way you're using this word, especially given that your entire comment is denying that the US is more obese purely in virtue of white obesity statistics.
If you are intent on finding offensive meanings you will be able to regardless of if they are there or not.
It's pretty clear that "seems" means that obesity seems to be a US problem unless you start looking at demographics, where similar demographics in different countries have the same rate of obesity (e.g. white people in the US, Australia, and Canada) and demographics in the same country have different rates of obesity (e.g. in the US blacks, whites, and Hispanics all have different rates of obesity).
I was not denying that the US is obese, to the extent that it is. I was explaining that it is not "American culture" that is the issue. Multiple groups that share "American culture" have different rates of obesity and groups that don't share American culture do share obesity rates.
Whether or not you actually meant it, this very clearly comes off as you saying that they aren't American.