My boyfriend lied to me about buying her a gift...why?

We went to the mall together and were picking out some snowman ornaments with our names on it. He was holding three, and I asked him, "how many did u get hun?". He said 2. I didn't question him because I thought I was imagining thing. When we were in line to pay, I double check everything we got, and accidentally picked up a snowman with a girl name on it. I was like "OMG..WTH". I realized he lied to me and hid it from me. He said he was gonna put it back and was trying to make me mad...obviously, he lieddddd! What's going on?