GP's point is that whenever you sell or offer something to users in U, you have to abide by U's laws in doing so - no matter whether you did that all while sitting at your desk in country C.
Whether or not enforcement or liability is realistic is up to the relationship between U and C I guess - my guess is France and Switzerland are on pretty good terms.
This is not exactly your focus, but this means that it can be possible for there to be a set of laws in U, such that an action is required and illegal if not present, but that this same action is illegal in C...
I.e., the predication is both meaningless and pointless, unless the supposition is that the laws of U don't hold - if C extradites a citizen of U over said action, is then U's law not supreme?