Job interview body language?

Im currently finding it very difficult finding work. I left my previous job a while ago to concentrate on my accountancy studies. I am studying for the AAT qualification and i am nearly AAT qualified. Ive had quite a few interviews but on 2 of them i noticed that when i tell them that im nearly qualified and stuff they get defensive and cross there arms over there chest as if they are on the defensive. Why are they doing this?