After watching that interesting video... I presume all this applies to Oscilloscopes that are powered via the wall socket? For example....
Attach your Arduino to the USB cable which is hooked up to your PC. - now attach the GND probe from an oscilloscope, to the + rail, it will "short" because it's shorted
to earth (as described in the video).
But my question is, if it's "Isolated" it's safe... does that mean ALL portable Oscilliscopes (not connected to the wall to power it) are safe?