That's not true. Places like Sweden, Luxembourg, Switzerland etc have higher standards of living.
US isn't by no means bad when it comes to standard of living, but it definitely isn't "higher than anywhere else in the world".
It depends on how you measure "standard of living", as it's actually pretty subjective.
In short, if you're a billionaire, you'll probably get the highest standard of living in America, living in a massive private compound somewhere. You'll have access to whatever food you want, the best medical care, etc. And if you're not a billionaire, you don't matter in America; only the opinions of billionaires matter there.