Most demographic information in the US (all?) is self-reported, and unless you were in the American southwest, Hispanic communities and influence on broader US culture is pretty recent, so I suspect not that many U.S.-derived Native Americans are mislabeled as Hispanic.

Traditionally it actually went the other way: Native Americans, while second class citizens in a lot of respects, were more respected than black people or dark-skinned immigrants. So, for instance, there were tons and tons of light-skinned black folk passing as Native and marrying into white families in New England especially. It was a big topic in genetics when things like Ancestry DNA reports became more common and lots of people who’s great great great grandfather was Cherokee or whatever found out he was actually an escaped slave who passed as Native.

That being said, most Latin American Hispanics are of at least partially indigenous descent, so in a broader sense most Hispanics are indeed indigenous, they’re just descended from Nahuatl/Mayan/Quechua/Mapuche or some other indigenous ethnic group, rather than one of the groups that is today considered ‘Native American’ in the US.