And that's part of the problem: it's small-talk, used as a silence-filler by people who don't know each other. The goal of asking is "say something I can relate to" - so in your example, you're hoping for "my dad was German" which you can follow up with "Oh yeah? I've been there twice! Where in Germany?" and now you have a vague, thin, irrelevant point of affinity between you and this total stranger.
The argument of the article is "don't look for affinity with me in any possible way, because everything you do as a white person offends me."