A tattoo artist doing this seems to me to be a good way to damage that artist's reputation. Why get a tattoo from an artist who has demonstrated willingness to sue over representations of you??
From the article, the artists claim that they were approached by a firm to buy the copyright to the tattoos for a clothing line and then once the deal was done, the firm went after 2K, they say they didn't actually intend for this to happen, and they don't own the copyright anymore.
So basically the firm acted really scummy, and probably intended to go after 2k the entire time, but sold it to the artists as 'clothing line'...Is anyone really surprised?
He probably thinks that he can get (relatively) FU money by suing.