Back when it was installed, the copper pipe "ground" was probably acceptable to the code, but it is not the best way to ground, it assumes there is continuity to the steel or whatever pipes outside and it assumes that those pipes have not been replaced with modern PVC or some other non-conducting material.
If they have been replaced, the non-ground ground would just bring the bolt inside - BOOM!
If they have been replaced, the non-ground ground would just bring the bolt inside - BOOM!
