Well I do understand your concern about a hoax.
The question I have is what is the hoax?
The rocks are what they are, they don't purport to be a map or a treasure or anything but what they are. There is no inducement to action or encouragement to believe anything in particular.
They are decorated by random cartoon figures and piss poor "Spanish" inscriptions on some rock from near Flagstaff. I don't see any "hoax" in that.
If you see other meanings in these rocks - good for you. At this point there are as many "solutions" and treasure theories associated with these rocks as there are seekers. I don't see any consensus on their meaning.
I think these rocks are accomplishing what they were designed for. To distract, delight and confuse the viewer. They have done that quite well.