No a faulty surge protector would not cause this.
It is fairly common I would say that pumps and heaters will have cracks and or exposed wire and corrosion, that lead to stray current and many people will use a grounding probe in their tank.
When using a multimeter to check for stray voltage you will see what so call noise, not sure if the technicical term but the meter will pick what appears to be sine voltage but it is just noise from pumps in the water stray voltage will register at a higher steady number. It took me awhile to figure this out.
I had a faulty heater once but it only put current in the water when it was on. So when Ineas checking with multi meter it read no current but when I stuck my hand in the tank sometimes I would get a tingle. It took me a little bit to realize it was ny heater