At least you do not have to think twice whether to buy new TV or not.

House grounding is not meant for lightning, unless you install lightning rod on rooftop.

How come there power leakage when plug is off. No such thing. The only way people talk about leakage is on appliance that is never off like when you off using remote or anything on standby. TV is one of them.

Your house grounding is to protect you from electrocution when touching faulty appliances with Live wire or AC short-circuited to appliances body. Protecting house from lightning means you need to install lightning rod on top of your house rooftop and have sizeable copper strip to grounding rod in the ground. House grounding wire is not capable to carry high current caused by lightning.

I don't deny what you were saying but my understanding was that he was talking about leakage when power is off unrelated to lightning. If you read about leakage, it is described as what I explained.

The electrical jump spark between two point I believe is not called as leakage but electrical discharge.

What type of voltage controller are we talking about here? Did the controller also get damaged?

I'm not sure what qualification this person has but his description is misleading. I would say it is not correct. The "leak" in this demo seems to me is not about switch leak. Even if you remove the switch and separate the two wires in the switch by few inches apart, you would still get the voltage reading. It has nothing to do with switch.

The phenomenon that we are seeing here is ghost or phantom voltage. Many people do not really understand the difference between voltage and current. It depends on the wiring in the wall. In my house also certain points even get 20V when measured with multimeter. This is the voltage reading but there is almost no power this voltage can supply. It probably can lit the neon indicator on the switch. That is why those switch with neon bulb still lightly lit up when switch is powered off.

The voltage on the wire is induced voltage by the live wire adjacent to disconnected wire laid next to it. In house wiring, you are most likely pull the L and N wire next to each other or they are laid together in conduit including the switch wire. Even when the switch is off, the AC on the L wire will induce the switch wire next to it and generate voltage. Same concept like transformer. The primary winding and secondary winding do not physically connect to each other but the voltage is produce at the secondary winding still. However, unlike the wire in the wall, there are many loops of winding wire that collect much of magnetic flux to generate power or current to power load at the secondary.

I bet if the guy use a LoZ (low impedance) multimeter, the voltage reading would be zero.