ike many carriers, United Airlines and Lufthansa operate a ‘joint venture’ where they share revenue for their operations across the Atlantic. There’s not supposed to be any difference between traveling on a United flight or a Lufthansa flight. Both airlines put their flight codes on the other carrier’s flights. That means United sells Lufthansa flights as though they were United flights with a United flight number, and vice versa.
But if Lufthansa is going to sell United flights as though the fights were their own, then those flights become subject to European consumer protection rules.