That's a very big question and probably only time will tell. Without getting into it too much, a very basic difference is..

Gas can explode like a bomb but (a) it needs an ignition source and (b) there can be visible signs when the fuel is leaking to let you know to take extra precautions (like spray fire retardant). You can actually get fuel on you and you'll be fine.

High voltage systems don't (usually) explode, but they have lethal amounts of energy stored that can find its way into your body if you complete a circuit. Furthermore in a mangled wreck there aren't necessarily visible signs when a component is electrified. You find out the hard way.

Basically Tesla deserves props for making an extremely strong car. That's what was tested here. But the spin is they're claiming "safest car" while completely side-stepping the high voltage safety issue.