These numbers are based on a Hill-HarrisX poll from Aug 2020 which asked “do you support a Universal Basic Income program to pay all Americans $1,000 per month?”.

To your point, there are a couple other polls that show lower support. Pew Research indicated that only 22% of Rep. voters and only 66% of Dem. voters support, but that poll is framed more negatively: “do you support a UBI for Americans *whether or not they work*?”

In the country as a whole, this is roughly a 50/50 issue. But the support from young people is overwhelming, and the recent trends are favoring UBI.