He really doesn't know yet. It's part of the pre-school stages of development to be able to do this. It does sound like he is left handed, I am not saying that, I am saying that most of my left handed friends do things with both hands due to it being handy...for example, scissors. My friend that is totally left handed uses right handed scissors due to not being able to buy left handed scissors in the 50's when she was in elementary school learning to cut. Others find similar things too.