A different thought: I wonder if the term portmanteau word makes sense in the context of German, given that concatenation is a standard mechanism for word formation, and thus doesn't represent anything unusual or noteworthy.
Well, I think that it could still be used in a broad and general sense, seeing that it just means blending two (sometimes incongruous) words together, but I’m by no means an expert on this matter (especially as it concerns German!).
Yes, I think "German portmanteau word" is redundant.
Reminds me of the German philosopher who toiled for decades on his three-volume masterwork. But it was hopeless, because he died just after completing volume two -- and all the verbs were in the last volume.