So even a marked and gated road is nothing to people anymore, it wouldn't surpirse me if someone such as the Kims would come upon a closed gate and open it and drive on through.
I doubt it. In your case, it was people who wanted to get to the top of the mountain. Their destination was beyond the gate, and that was likely the only way up.
In the Kim's instance, however, I doubt that they were going sighseeing in the dark up poorly-maintained roads. It is more likely that they thought that the route was a short-cut. Had the roads been closed, they would have probably just gone around.