Huh? He said what?

So the other day I was reading a book about World War I to dd, 4th grade. It's definitely not the most interesting book in the world. I mean, she doesn't beg me to quit reading it, but she doesn't jump up and down and beg for more chapters, either. That's ok. I told her it's giving her a hook to hang further info on later in life when she covers the World Wars in more depth. Anyway, so back to Mr. Smarty-Pants, ds4, sitting quietly building with Legos. I was reading about America's officially getting involved in the war, and how we set up factories in Europe to produce things needed to support our troops...including a candy factor. Mr. S-P pipes up "Wow, I didn't know there were candy factories back in 1900!" OK, obviously HE'S getting some hooks to hang further info on at a later time. I thought it was pretty good that he picked up on the general time frame we were talking about (precise dates DO escape a 4 y/o, LOL) and that he realized we were talking about something that didn't happen recently. I swear, he's too smart for his britches!