Hi Why do you think John was taken aback when Sherlock says those were his parents? It's a similar reaction to when John finds out that Sherlock has a girlfriend, like he can't handle the moments he realizes Sherlock really is a normal human being.
That's about it. It seems Sherlock had never mentioned his parents to John (in the two years they lived together!), or maybe just in passing, and there must be no photographs of them in the flat. (Bad son, Sherlock. Call your mother. She worries.) They weren't at the funeral, of course. I don't know if it's John can't handle him being a human being--he knows Sherlock is a human being, even if he doesn't act like one sometimes--I think John is mostly surprised that out of nowhere Sherl's parents are in the flat and they're normal, not aristocratic supergeniuses or something, and Sherlock is hurrying them out the door as if they don't exist. John had had a lot of surprises to deal with over the past few days and now he gets one more, a glimpse of Sherlock's family life that is so different from Sherlock and Mycroft.Â
