> European companies selling only to non-European customers don’t have to comply with GDPR.

Usually they do. European company processing personal data of non-EU customers falls with article 3(1) "This Regulation applies to the processing of personal data in the context of the activities of an establishment of a controller or a processor in the Union, regardless of whether the processing takes place in the Union or not."

Of course if they do not process any personal data then it wouldn't apply but that's pretty unlikely (and if that was the case the EU customers data wouldn't fall within GDPR either).