Looks like the engineman on one of the trains either forgot his last signal, or forgot about what was on his paperwork. It happens.
Unfortunately, it was the _other_ engine guy who paid with his life.
Actually, my understanding is that the Swiss take their railroading quite seriously.
But regardless of the best efforts, things go wrong. One can follow procedures, and _still_ have things go badly awry -- look at the one-man oil train runaway up in Canada not long ago.
Or consider the high-speed wreck in Spain. This wasn't some rookie at the controls -- it was an experienced operator who -- in the course of [what was probably] an official conversation with the dispatcher/controller -- lost his sense of place, and forgot to brake for the curve he was approaching. Too late, when he realized what he had missed.