It's a term of art that straightforwardly means people who embrace AI-assisted programming. As opposed to the very large number of engineers who actively don't like it, or have enough change aversion to have avoided it.
AI-native should mean those who were born/came-of-age/started learning programming in the era of mature AI. It shouldn't be many people (relatively speaking) at this stage.
The term that best suits "people who embrace AI-assisted programming" is AI-first programmers, which is what they literally mean by the looks of it. Clearly, they just use what they think sounds cooler.
If they wanted to discriminate on age, they wouldn't need a term for it. Big tech companies have been doing it with things like college interns or paying for student loans.