But the TMG as well as the BDSG are federal laws and after reading his paper I would agree with his view of them.

It would only take someone to go to their local data protection supervisor (Datenschutzbeauftragten) and complain about being tracked by the facebook like button on a site hosted in germany, the data protection supervisor would have to issue a fine (if he agrees with that interpretation of the law) and it would go to court, since the owner of the website would naturally dispute it.

Difficult to say how the court would rule.