Be interesting to see if it is 'step potential' that was the issue Ligne Jaune line incident.
It's more likely they stood on the third rail, or one did and the other ran the wrong way. This line and the St Gervais-Vallorcine one (via Chamonix) are both 850V third rail and run mostly in mountainous terrain where the line is unfenced. Even where it is fenced, it's often only a token effort. The two Google Earth views, of the outskirts of Chamonix and a Pyrennean valley (where there's a bit of a pixel shortage), show how accessible the track is. Stations improved more recently may have better fencing, but still have a foot crossing to the platform.
Both lines rely on protecting only those places where people can get at the line, and at stations use wooden planks as well. On St Gervais-Vallorcine the planks are above the rail and wider, on the Ligne de Cerdagne they are on both sides and only a little taller. There was a case not long ago on the Ligne de Cerdagne of a child touching the rail and getting burnt, but not seriously hurt (so presumably the leg that touched was stood on the ground at the time). This was at a point where an unofficial footpath had been made to get to an (equally off-limits) open-air hot water pool made suddenly well-known by social media. The local "public outrage" following called mainly for fencing (railway or pool), a new footpath, or closing the parking on the main road nearby.
That said, I could find only one recent report of a human fatality, so presumably this approach is quite effective.
