No, they're free-riding. If drug companies can't charge higher prices in the US, they will do less drug development. Everyone involved in the business/investing side of pharma knows this; it's not even an argument.
If you and me both buy the same car, but i'm better at negotiating than you and get a lower price, I'm not free riding because you 'funded the design of the car with the extra money you paid', you are just bad at negotiation.
When we all negotiate lower prices, we get fewer new drugs. Maybe that's better than the status quo (for Americans). Maybe it isn't.