This for me does not make sense as a copyright violation. It’s like saying that Adobe is in trouble because you drew something infringing in Photoshop. If you prompt the model with the intention of creating something infringing by mentioning the name of the characters and the work, and you get something infringing out, then it’s you who have infringed the copyright, not the maker of the tool.
Did you even read the post?
But also, the argument of 'user responsibility' doesn't hold up on its own regardless (imo).
If I make and sell a toy printer that can only ever produce 3 pictures, and all of them contains copyright materials, would you really say that it's fine and responsibility falls under the end user? And I could sell that printer without any issues?