I felt the same and wondered what the right answer would be. I generally haven't interviewed at companies where I didn't know enough about them to be excited about their domain, and then be excited about their domain, but ultimately as a dev they pay me to write code so I want to also be at least as, if not more so, excited about doing that.

I guess the right answer, if the goal is honesty here, is to couch it in terms of "I'm mostly excited about <your problem domain>, but to be honest one of the reasons I even decided to go this far in the interview process is <tech feature>" or something? I'm not good with people, so I'm as much thinking out loud here and asking for feedback as much as asserting what I'd do.