This guy is a writer , what kind of merch can you be selling and believe it was your creation. He was selling posters, T shirts, cards, all must have someone else's artwork. Seeing how he didn't even create the original images he would still is stealing someone elses original work. Who he should be most pissed at is the attorneys who didn't tell him well enough he is an idiot for tying this lawsuit.
I know I see artists selling sketch books , and original images, commissions but very few are selling mass produced prints and if they are they could have legal permission to do so. Some do and they are told not to, and I would bet if any of them are stupid to go after the license holder in court they will get hit too.
I know with other licenses there are artists who constantly break the rules and have yet to have legal action taken as its not worth it to the license holder as its a small fish in the grand sceme but is talked to all the time about what he is doing and gets better for a while then goes back to old habits.