Found very quickly during hot check

I'm no electrician and I could tell what was wrong with a 2-second glance.

So what happens if it's wired like this?

You can touch this! ....but it might hurt.

whelp, now it's hammer time

Not an electrician or even electrical savvy but it's typical for ground wires to be bare. Its not typical or good or even sane for them to be connected to something which WILL carry electricity.

Bare wire for grounding purposes. That's all it's used for.

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.

Wiring hot directly to ground will create a short circuit. Ideally that causes the breaker to flip immediately enough to stop anything bad from happening as the amperage jumps. But it can melt wires, fry electronics/outlets/switches, cause sparks to fly, create a shock hazard, or start a fire, yes. The breaker is there to "ideally" prevent that, though they can fail. I'm also not an electrician by trade so I'm really not sure, but i wonder too if one could fuck up the wiring bad enough to cause a short in parallel to the breaker that doesn't even trip it. If old boy is sticking the ground wire into hot switches, I would question what other dumb shit he might have done.

"attempted murder", now honestly what is that? Do they give A Nobel prize for attempted chemistry?

Ground is bare in the US/Canada in residential wiring (insulated grounds are only found when pulling wire in conduit or in isolated ground systems like hospitals). Guy who did this is just an asshole and doesn't know how a 3-way switch works.