I should never watch youtube, but I did and I saw this possible error. The designer's initials below the saguaro are usually plain to see. In this possible error, the cactus below the saguaro covers the initials. This was difficult to photo, but I think I captured it. OK piranhas - go!
Yep this looks right to me, I have one of these so-called Extra Cactus varieties but it's well known that it is just an interesting die chip location. Off the top of my head I can think of a couple other such named die chip varieties; the Delaware Spitting Horse quarter, the Nebraska Homestead Leaky Bucket quarter, and the Sacagawea Wounded Eagle dollar.
Wanta bet if you search threads back in 2008 you find the first post on this state quarter. Varieties finds.