Is there any evidence that this pottery was being traded across the Limes into the Roman Europe, or is it only found in barbarian territories? Certainly, we have considerable evidence of trade across Hadrian’s Wall in Britain, but I know nothing of similar trade in what is today Germany and Poland.
You're onto something there, Roman goods had a deep penetration in areas not ruled by Rome. This stuff was of a style and date that corresponds to the Vandals, a Germanic tribe that eventually spilled over the border and sacked Rome, then went on to northern Africa, founding (not surprisingly) the Kingdom of the Vandals.