Well it depends triple. If the guy knew that he was using the improper materials for fixing the DC-10, then that is reckless behavior. No different than using bogus parts.
You have to differentiate between an honest mistake and willing non-compliance to save a buck or cut a corner. This applies to everyone in the aviation industry. If you willingly violate established procedure you might at some point be held liable for your actions.
Now if he was following company established procedures then that is a different story. Don't know all the details, but I would assume that since he was given the blame that he was acting on his own accord or that he at least knew the repair he was making was not following procedure.