I'm not surprised at all. ThinkPads are legendary for their toughness. This comes from their build technique perfected over the years. Probably best shielded laptops I've seen. They did this years before anyone else bothered. It would be very hard to break that Faraday cage.
On old models cases were basically metal parts covered with this characteristic rubbery plastic. From inside it looked like this:
Right now after Lenovo took over they moved many of them to plastic, but they are still well shielded. This is T40 that is being tested and most laptops are like that inside:
And something like this is behind T60's screen:
Don't let me started on those magnesium frames
People are right now praising shiny aluminum toys from fruit company, but IBM was making the best laptops and sending them to space years before them. Even Chinese Lenovo didn't destroy them much. It is simply business workhorse. ThinkPad is Fluke of computing world.
Since we are talking about high voltage and electronics. Check this out: