Boyfriend lied to me about how much money he got for christmas

So his grandparents sent us both Christmas cards with a check. They sent me $100 and him $600. Extremely sweet of them. They didn’t need to send me absolutely anything.

What I’m confused about is this: We saw each other open our cards but he didn’t realize I saw his amount. I said I got $100 and he said “same” and then closed it. Why lie? He’s pretty private with his money in that I don’t know how much he makes or has saved which is fine but I don’t like being lied to. Is him lying something to bring up or do I just leave it?

I’m not after his money, I have a great paying job, we pay everything absolutely evenly, I don’t ask him about his finances. Just the lying part really bothers me. Am I being a baby about this?