The largest category consists of independents, who form 42% of registered voters. Independents have consistently made up the largest category of American voters for decades.
The articles is referring to polling which is taken from what people tell the pollster while this article refers to registered unenrolleds (called independents here). Does the poll ask you how are you registered our which party you identify with?
It's interesting, as I am able to and do look thru a long voting history of population segments, that party leaning is EXTREMELY obvious of the unenrolleds. Indeed, party registration cannot be faked (other than a few dedicated "operation chaos" adherents); with primary ballots taken and considered along with attendance record, an analyst can get a strong feeling about a voter and a voter population.