Here's a thought/idea -- ask your Indy to pull/check the DISA, probably only an hour of labor. If the DISA flapper lets go/breaks it can potentially get ingested in the intake system, maybe a piece of that butterfly flap broke and went thru the intake valve on cyl #6, a couple strokes of the piston and it hit the spark plug mangling it like your photo. It's just an idea/hypothesis, I've never heard of one single valve breaking off into a cylinder on a BMW but guess that's possible too.