Many of the ppl at various registries don't know or care.
Had one a while ago would happily have street registered my son's CRF-50.
When I said; no - off road only, he said; oh, it's a quad...
BUT, be ready to show mirrors, signal lights, etc to Fish n Wildlife or police.
Big thing for me and others is IF your insurance company would disavow you if anything bad ever happened.
I don't have much faith in them, personally.
Tell your buddy to crawl out of the 90's and buy a KTM.