60A circuit - what failed?

~20 ft dedicated 60A / 240V circuit for gen 1 Tesla high power wall charger. It runs directly out of the top of the breaker box inside the wall to the ceiling/wall above, into the pictured junction box, and then into EMT mounted to the inside of the garage wall. Installed ~11 months ago by licensed electrician I’ve used in the past.

I plugged the car in last night and after 20-30 minutes of charging the car tells me charging stopped to go check the issue. The circuit breaker is flipped, I flip it back (with a wooden bat, carefully), immediately flips again. Don’t see any obvious damage in the circuit breaker box after removing the break box cover. With the breaker off, I opened the wall charger up to look for any obvious signs of damage. Nothing.

Flip the breaker one more time, get a nice pop, spark brief puff of smoke from the pictured junction box. Circuit breaker does not flip. I turned it off out of an abundance of caution and walked away. Took these pictures the following morning. Presumably heat melted the cable insulation and shorted against the metal door on the face of the function box. The completely obliterated wire nut also seems like a source of failure.

What failed (the physical install, materials, something else)? Was the failure expected based on visual evidence? How to prevent this failure when this gets fixed?

I have a 1 year warranty on the work and materials but not sure if I would hire them back to create another ticking time bomb.