That was probably the worst explanation of 'theory of mind' I think I've ever heard.  'Theory of Mind' is the recognition that other people have minds which are separate from your own.  Very young children (like 1 year olds) do not have this.  It can actually be tested by telling them a simply little story and then asking them a question.  You tell them that there are 2 girls (or boys, whatever) in a room and they have a toy.  They hide the toy under a basket.  Then one of the girls leaves the room.  While she is gone, the other girl gets the toy out of the basket and hides it in a box.  Then the other girl comes back into the room.  The one that left is then asked to get the toy.  Where does she get it from?  Children with no theory of mind will say that she goes and gets it from the box because they don't understand that since she wasn't there when the toy was moved that she couldn't know where it was.  Children with a theory of mind would realize this and say that she would check the basket and then not be able to find it.  I believe most kids develop this theory of mind somewhere around age 3.  It's a very important psychological milestone.