The article doesn't mention US citizens specifically, just US adults. But yes, the context and link make it clear it wasn't talking about South America, but even if it were, there's a table in the article that has a list of countries literacy rates. A cursory glance shows Mexico, Brazil, Colombia, Ecuador as having higher literacy rates than the US.
I don't know how accurate these stats are, but it's interesting nonetheless.
The average American reads at a 7th- to 8th-grade level. 21% of Americans are functionally illiterate. https://www.crossrivertherapy.com/research/literacy-statisti...)
It's not an insult, it's just a fact. And it's a problem for politicians who need to communicate complicated policy proposals.
Americans aren't getting smarter, so politicians need to adjust the policies.... which is how we get "build a well" and "drill baby drill."