Wrong law, wrong discussion
The Berliner Kammergericht didn't use the the data protection laws. It applied the socalled Fernmeldegeheimnis (telecommunications secrecy) to the Facebook-communications, which forbids the unauthorised interception, suppression, exploitation or defacing of telecommunications messages, which include telefone, wireless communications, telegraphy, telex and similar communcations. Under another law, emails also fall under the telecommunications secrecy. The Kammergericht just chose to view Facebook-Postings as Emails.