CA registration question

I recently purchased from a private seller a motorcycle that was never licensed in CA, it’s a 2017 and has 1000 miles on it. The DMV wouldn’t let me register it because it didn’t meet California emissions standards or something. So is it true that I can’t register this motorcycle no matter what?? It’s completely stock but just doesn’t have that one sticker saying it’s up to CA standards. Is there any way around this? Also, was the guy who sold it to me legally allowed to do so? via /r/motorcycles https://www.reddit.com/r/motorcycles/comments/e9zxw5/ca_registration_question/?utm_source=ifttt