What does it mean if a guy is nervous to hug me?

What does it mean if a guy is nervous to hug you, but not nervous when it comes to hugging other girls? He'll give me briefly short side hugs sometimes and that's all. He said so himself he's nervous. We never had a frontal hug yet in months of our friendship. This isn't really a big deal for me but I just want to either one of us to readily initiate a frontal hug.