According to the same research, 1% of US adults are Buddhist, and they fall in a separate cathegory.
All the polls are weird, and very much depending on how you ask the question and how you slice the data.
But you're right, the word atheist carries some baggage in a christian nationalist country, but that was kind of almost my point. So many people are afraid of the word atheist, but are "not religious, don't believe in any gods, don't follow any practices", which is, actual textbook definition of the word.