This isn't excatly the same but I do the same thing. At school I am always focused, very involved (not always speaking wise but activity wise), and if I am with people I am comfortable with sometimes silly but still reserved. When I am by myself or at home I am super quiet but always moving around and doing very unproductive things. I'm not doing a good job at explaining this...but I do the same thing, and I think it is normal I see a lot of people do this, they are different depending on where they are and who they are with.