The head is flat, it forms one boundary of combustion. So it will be running a "Dish top piston" to form a combustion chamber
The outer flat rim of that piston runs very close to the head at TDC. the valve spring does not have enough stored energy to slam that valve shut and punch out that missing shape(valves and seats are very tough). if there were a foreign body some how come through and lodged between valve face and seat that wide rim on the piston would have smashed the crap out of the valve, yet there is absolutely not one bit of witness on the carbon on the valve head to that effect. If it were a foreign body there would be witness all over the joint.
I know your only getting second hand info, so are we, makes things difficult for all.
If it has been dealer serviced Johns advice of going to a dealer rep is obvious and sound, but hard if they are stranded miles from no where? without premium road side assist? it would be a hell stressful time for them