Trying to read that comment charitably, I honestly can't ascribe a motive to the "surprise". I've often stated I was "surprised" to learn something that was particularly detailed/nuanced in an area I already generally had fairly deep knowledge, especially if it revealed a new history or layer of depth I could integrate into my base knowledge.

I'm not saying that's definitely how I interpret it, but it's definitely a reasonable possibility. And I guess I wish more people here would at least try to read others' comments more charitably. At worst, your assumptions are right but you gave an opportunity for the other person to be better understood and for your own frustration level to pause before rising.