Welcome, Germanist. Hope you find other discussions here interesting enough to stick around and join in. For what it's worth, I think every contributor here has felt that slightly disconcerting sense of alienation from their mother tongue at some point - even if we can't always agree on such a clear cut reason as in this example you quote. I agree - this book seems like a spurious trawl through secondary source material, just in order to find sensational sounding cases of strange language.