Explaining things

Noah has gotten really interested in explaining things to me. He will take a toy, that we have had forever, where you pull back a spring mechanism and then it locks in place and you push a button to shoot out a car.
"Baba, you see it. You have to pull it back this one all the way like this. Then you have to push the button and it goes voom. It goes out like that Baba. You see it?"
In fact he's been asking me the same questions everyday. Like why does the stroller bump on a bump. But he's not asking me because he wants to know. He is asking me because he wants to hear my explanation. Then he will ask me again and I will get frustrated and say that I already told him my answer, so what was his answer. He will then try to copy exactly what I just said in his own way. At first I thought he wasn't listening to my explanation and that was why he asked me again right after I answered him. But obviously if he can say it back to me he was paying attention. In fact he is probably asking me twice so that he could memorize my answer. That kind of makes me nervous because I was just giving an answer off the top of my head to keep him occupied.
Anyway every dusk, he also asks me why it's getting dark. And I keep telling him the earth is turning away from the sun etc. Sometimes I accidentally say the sun is turning away from the earth and then when I correct myself he gets really mad and says, "No the sun is turning away from the earth." I usually defer to the Cat in the hat episode we saw or the Dinosaur train episode we saw which deals with this question.
I also tried this little trick to get him thinking and also to give me a break from talking where I simply say, "I don't know what do you think?"
After a while he started using the same trick on me so it doesn't work anymore. The truth is too, I also want to know what he thinks. If you just say, "the earth is turning away from the sun." well that's just a bunch of words really that don't mean anything. And even if you accept it as true, you will still probably say the sun went down and indeed still think of the sun as moving instead of the earth turning. After all that's what you are seeing right? Just repeating that the earth turns doesn't mean that you understand what that means does it? So it takes some more thought and unless I know what he thinks and how, then it's difficult to know how to explain things.