It’s “Native or Bilingual” actually. It means that it’s either your native language, or a second language that you speak with the same level of proficiency as a native, thus making you bilingual. Since theoretically both a native and a bilingual person would have the same level of proficiency, they opted not to make a difference.
This in turn is probably related to them willing to be able to use language proficiency as a filter down the line. Imagine you’re a customer and want to deal only with sellers who are highly proficient in a certain language. Since (again, theoretically) a native and a bilingual speaker have the same level of proficiency, you’d select “native or bilingual” in your search. Having a customer selecting either native or bilingual would be unfair (as in, why would someone who speaks like a native be discriminated against just because he wasn’t born speaking that language?).