Caution: bragging mom ahead, PROCEED WITH CAUTION

Ok, so Alex and I do a lot of fun learning activities together, and with that has come math. I've always noticed that he's had a knack for math, he's always just "got it". The concept seems to come very natural. So yesterday during our busy errands, we're driving down the road, he's in his carseat and out of the blue he says "momma, I know what 20 minus 10 is."
me: "Oh really!"
A: "yeah, it's 10!"
me: "Wow, Alex, that's excellent. So who taught you that?" (cause it wasn't me)
A: "Oh no one."
me: "Wow, you are just sooo smart!" I say, while in my head I just KNOW there's no way he's figured this out on his own... we do math, but haven't even touched on subtraction. Sure it has come up, but only in a very practical sense.
A: "I know 10 plus 10 is twenty, so that means 20 minus 10 is 10."
me: <<>> "WHAT!?"
A: "Yeah, and 10 minus 5 is 5 because 5 plus 5 is 10."
me: <<>>
A: "And 2 minus 1 is 1 because 1 plus 1 is 2."
me: "Holy cow Alex, that is excellent!"
A: "Am I right?"

The kid goes on and on to tell me more and more subtraction and with every answer, explaining how he came up with the answer.

Looks like we're going to have to start searching for his real parents too.