ROFL.
Yes, not saying it isn't ceramic but no one has actually proven it to be that.
Keep in mind that you are talking about dust, not chunks, and when a turbine wheel comes off, what happens to the comp wheel? It starts machining the housing away at the front. This creates dust also. What happens to alloy dust when you burn it? It looks like what you'd imagine ceramic to look like.
Theories of engines sucking blades back into themselves is a bit far fetched. Can happen, I'm sure, but you guys all make out like it's going to happen to every single GTR turbo that ever existed.