Why is this camping light deadly?
Most outlets aren't polarized.  Even in places where the outlets are polarized, mistakes happen.

There's a straight connection between the outlet and the ground of the USB port.  All there is in between the two is a diode.

If that wire is connected to neutral in the outlet, then nothing bad will happen if you touch the USB ground.

If you plug it in the other way around (or the polarized outlet is wired backwards,)  then you have the full line voltage on the USB ground.

That can be deadly.

Additionally, even if it is connected the right way around, all that's between you and line voltage is a capacitor.  

If it is a Y rated capacitor and it fails, then you are safe - Y rated capacitors are supposed to fail open.  They almost always fail open, but do you want to bet your life that a company that builds a capacitive dropper powersupply with user accesible connections will also think to use a Y rated capacitor?

Even if it doesn't kill you, it can destroy any laptop or other USB source you connect to it.