I get your point, the claim was incorrect. But if you're only beaten by Salvador, Cuba, Rwanda, Turkmenistan, and American Samoa... Well, maybe the overall point stands: "Highest in the world" is hyperbole, that much is true, but the USA has an insanely high rate of incarceration, higher than most countries, and definitely higher than all "developed" countries. As a point of comparison, the next OECD member on that list is Turkey, which has about 34% fewer prisoners per 100k people than the USA.

Assuming the accuracy of that source on the numbers, its actually the 5th.

Yes, the United States is the sixth listed, but the 5th listed is part of the United States, not a separate country. (So are several others, but I don't think Guam or the US Virgin Islands are big enough that they move the US overall rating down far enough to matter.)