I am no expert in German copyright law! But your own source says:
"It is worth noting that the result would stay the same if CC0 would not even contain such an explicit fallback rule. According to the prevailing opinion of the legal scholars, public domain licenses (which cannot be interpreted as a waiver of rights under the German copyright, see above) are reinterpreted as unconditional, unlimited, non-exclusive (i.e. public) licenses."
which appears to contradict your statement that public domain dedications are treated as no license at all.
"It is worth noting that the result would stay the same if CC0 would not even contain such an explicit fallback rule. According to the prevailing opinion of the legal scholars, public domain licenses (which cannot be interpreted as a waiver of rights under the German copyright, see above) are reinterpreted as unconditional, unlimited, non-exclusive (i.e. public) licenses."
which appears to contradict your statement that public domain dedications are treated as no license at all.