I call bullshit on TFA, because last time I checked the german speaking area was culturally diverse in the traits mentioned.
Repeating stereotypes: people in Vienna don't yell and call bullshit on people (they are more likely to talk behind each other's backs), while people in Berlin yell at each other all the time to resolve conflicts (which seems way more healthy to me). These are stereotypes sure, but not more so than the ones mentioned in TFA.
So if there's no uniform behavior identifying even stereotypical german speakers, how can this guy pick up on behavior that is different just because of the language?
OTOH, hanging out in a culture that is more verbose (or not) about their conflict resolution can surely change you. But that's independent from language.