The metal on that light switch would be live any time the other light switch (on the other end of the red traveller wire) is turned on.
If that box is metal, it would make the metal brackets of the other switches live as well, and assuming one of the other switches is properly wired, it would just go back to the panel on the ground wire.
I think that would either complete the circuit and the device would turn on, or it would ground the circuit and pop the breaker. The same would likely happen with this switch as well considering the ground is wired on the hot terminal.
I'm also not an electrician so this is a full-on guess.