Looks to me like something is scorching the wall. Could have been something inside the cabinet, like putting away a cast iron pan while it’s still hot, but my guess is you have a screw in the wall there that is screwed into a shorted electrical cable.
I could definitely be wrong, but I’d cut a hole and see what’s back there anyway.
I agree about cutting away the drywall. Easy to fix after, especially since inside a cupboard. I would avoid touching with metal and wear insulated gloves I think.