Yes, surely a relay could have prevented this. I did a little googling, and since fast chargers can deliver up to 350kW, it does appear that a breaker rated for that power could be pretty expensive and large (e.g. full panel sized, $1,000). But that’s just a wild guess. Still cheaper than a couple years of insurance payments.
It's kinda weird in case of cars. The "PSU" (the device that converts current and voltage and sets the right value for charging) in case of AC charging is in the car, but for DC charging it's pretty much "car asks for that much current, charger provides".
So DC charger going haywire could damage the battery, and say DC charger putting high voltage on the control lines could also do some damage. Protecting against both is possible, just adds cost