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.