That's a really good catch. It looks like that 28% figure is specifically Level 1 or below in English literacy, which makes that number a whole lot less interesting for evaluating education levels.
I care about ability to comprehend text in someone's fluent language. The PIAAC figures don't appear to measure that.
Do you care about trends? Like an increase from 19% to 28% between 2017 and 2023?
Sure, but if that trend turns out to be an increase in non-English speakers it tells us less about the state of literacy, which is the thing I'm interested in here.
The national results page literally has a section where it shows separate results for native-born and non-native born participants. You claim that you're interested, so it's strange to see you speculate about what "turns out" when the answer is so conveniently available.