He says I’m not an open book.. what does that mean???

What does that even mean? Yeah I do keep things in. We’re talking about how I went on a group trip with my friend and her husband and his guy friend which is my cousin 🤦🏽‍♀️ I see where he coming from with the other guy going because he didn’t know that was my cousin. I don’t know how to reply to this please help me out.