He won the lawsuit on the grounds of Recklessness.
That means the company who provided the range knew that its gas connector is lose and it can be dangerous for the buyer, but the company didn't bother and dealt it with carelessness and made a severe negligence. This carelessness resulted in the severe injury of the buyer. So he was on the right to sue them for their negligence and lack of care. Thus he won the lawsuit on the grounds of company's recklessness.