The fish might be reacting to vibration or just movement in the room. One way to test this would be to have the lights in the room totally off and the only lights on are those in the tank.
This in essence should blind the fish from seeing to far away from the tank. Kind of like if your on stage and you cant see the audiance cause of all the stage lighting.
then you can leave the room and walk back in like you normally would after a period of time and see if you get a reaction. You could repeat this step with the room lights on to see if you get a different reaction. You could try to have your dad or someone else enter the room like you would and see if they react to the vibration of the steps on the floor or the movment of something infront of their tank.
I think fish are like the dogs in that socology expermint by pavlov (sp?). They get trained to respond to a condition. You or anyone else for that fact infront of the tank usually = food so they act accordingly when someone is infront of the tank. This is possibly one of the reasons beginners always feel their fish are hungery cause every time they look at them they are all over the front of the tank and top.
Note: these are just my observations and views. They may hold no water at all. (pun intended)