Isn't it still just possible that he's another Euro-skeptic Brit who can't abide the idea that his ancestors were Krauts?

The thing about Basque, and other language isolates like Sumerian, is that it attracts all kinds of crackpot linguistics. From what I remember, there's not much to Aquitanian other than some names, place and personal, but it is uncontroversially accepted as an earlier version of Basque (see Larry Trask's prehistory of Basque. But the Aquitanians, at least, were located georaphically close to the Basques. Theo Vennemann has a theory about a Pan-European language, of which Basque is a remnant. Europe's a pretty big space to be monolingual during the stone ages though. Whenever I read about language and genetics I have a suspicion close to hand of what the alternative motives of the writer are. Historical linguistics is unfortunately comingled with a lot of racist blather, especially in its early, 19th century years. So, yes, perhaps Dr Oppenheimer has some problem with German ancestors ...

Ceci n'est pas un seing.