I really do not view these as a double error personally. An error to me is something obvious like a misspelled hologram, flaw in the coin, etc... To me he just printed them off center a tad not really seeing how that adds value?
I agree..In the world of Philately that is stamp collecting..an inverted image, inverted color, misspelled words are true errors. Case in point is the inverted Jenny, or inverted biplane of which only 100 exist that command over $800,000 in auctions.
If there was a color shift or misperf we call them freaks or oddities. So for me the misspelling of Casascius with the missing S would be a true error..just because the ink is slightly higher or lower or sideways is not truly an error.
But that being said, if physical Crypto coin collectors place such a high price on this type of shift in printing, then they create the market value whether its a true error or not.