I'm guessing they booked it directly through the Norwegian Air website; I don't think they booked car rental at the same time, and pretty sure they didn't book accommodation or anything else. They must have used a credit card (although for years they didn't want a credit card so it's possible...
Just out of interest.....
My sister and niece are booked on Norwegian, flying from Gatwick to LA on March 31 (and then driving to visit me in Phoenix). Now, they almost certainly won't be coming (for obvious reasons). But if Norwegian go bust, will they have any recourse to get all or some of...