Given certain conceptions of what desire/preference means and certain assumptions about the transparency of mental content it might follow that you can't be wrong about desires (to wirehead and otherwise). But that hasn't been shown in the OP even though that seems to be the claim the title is making.

Yes, (like I've stated in the other comments here), if you use a more broad definition of "mistaken about a want", then we can easily conclude that one can be mistaken about their wants. I thought the narrowness of the definition of 'want' I was using would have been clear from the context, but I apparently succumbed to the illusion of transparency.