Sounds to me like he is just scared that when you leave his sight, that you are going away longer than a 30 sec pee break. When he loses sight of you, he rings the bell because he knows that usually you come right away, let him out and everyone is happy. I don't think it has anything to do with actually having to pee.
If I am in the house, mine has to be beside me at all times, 30 pee break or not
Just my two cent take on it.