The aero.de article linked in post #1 cites Air Berlin as saying that it hasn't received any passenger complaints.
I expect the LBA is investigating because the manouvre has been all over the media; it remains to be seen if that is merely a formality or something more serious. The
Berliner Zeitung is reporting today that the LBA has asked Air Berlin for a statement/explanation, and that Air Berlin has suspended the crew from service, as is standard procedure when an investigation is ongoing.