bearfoil:
That piece of disc scored the concrete, then penetrated both left and right casings at the exhaust nozzle to protrude out the cowling (Right side) of the cowling (#2).
In fact it penetrated the cowl (LH), the left side of the core nozzle, the nozzle plug, and stuck in the right side of the nozzle and cowl. This is all fairly lightweight material compared to engine casings. It didn't affect the #2 engine proper, although the implication of possibly inducing a second engine failure is obvious.