High voltage direct current is superior in many ways to alternating current, as it has no losses from impedance, but the arcing problem is a severe one -- high voltage DC has no "zero crossing point" -- so ultra-hot plasma arcs can be hard to extinguish with a poor connections.  Normally, when you break alternating current, every 1/120th of a second the voltage drops to zero, which means plasma arcs are not sustained for long in a broken connection with an air gap. But that doesn't happen with direct current. Of course the fault could have been purely resistivity without plasma arcing -- a poor connection could have increased resistance in the line and created heat, and that can happen with both AC and DC.

Mechanical DC switches -- even at low voltage -- have to be built quite a bit thicker and have wider gaps to extinguish plasma arcs compared to similar AC switches. Transistors are much better at breaking DC arcs. The bad thing with transistors is they have a voltage loss, which means electricity is wasted as heat. The 200 amp DC relay in my truck between the batteries makes one hell of a clunk when you disconnect the load. It has to disconnect and connect quickly, and over a decent sized gap to minimize the time the plasma is burning the contacts. And that's only at 12-15 volts DC, where the amount of arcing is limited. This Technology Connections video does a good explaining why switches go "click" and why it's good thing -- you want switches to open and close quickly to break the connection fast and extinguish plasma arcs that burn the metal in the contacts. https://www.youtube.com/watch?v=jrMiqEkSk48

But regardless, an interesting video.