Here's a couple of pictures that Lone Gunman took and showed us on the Chat.

The remains of a Square D Q1 2100

These pics were sent to the customer, the owner of the property, who was in another State.

Aah- the value of a digital camera

Wow. What happened to cause this meltdown? Aren't such failures very rare for SqD products?

Looks like some of the neutrals got damaged as well, 2nd from left and both on the right.

Did this require the whole can (or interior) to be replaced or is that buss tab replacable?

I replaced the whole panel. No idea what caused it to burn up.

May be a rectifier diode from a full wave bridge failed in a high power dc charger, or other equipment and a dc riple ended up on the mains.
Hence the braker had to interrupt dc and a arc remained for longer than expected?

Without any other information, that top breaker looks fried and the bottom one looks ok. Ditto the breaker tabs in the box. Perhaps a high resistance developed in the top breaker. I've had fuses develop a high resistance without going open, the same could probably occur with breakers - even Square D.