Opinions please!!

So I have been talking to this guy for the last 5 months. He is 20 and I am 18. I really do like him, and I am starting to fall for him. Today, we were in the car and “Marry Me” by Jason Derulo came on. He turned the music down and said “ If I asked you to marry me tomorrow, what would you say?” And my response was “No, but you wouldnt ask for me to marry you anyway”. He said “Fine, I’ll never ask you to marry me then”. Was I wrong for saying that? And why would he ask me? Not to mention, if he was actually serious I would have said yes.