I think it was a combo effect. I thought I cleaned the drip tray and dump trough after my last brisket, but probably not good enough. The belly was good and fatty, so there may have been more juice than previous runs. And there seemed to be more dust in the pellet bag when I was filling the hopper. So this may have led to it throwing more sparks than normal with the blower. I have sifted pellets previously to reduce dust, not this time.
So - I will clean more thoroughly, sift my pellets, and buy less fatty belly (the last one will not happen).
On a positive note. After cleaning, I ran it up to 500F and back down, no issues, then smoked a lovely slab of salmon (not pictured). It worked like a charm. So the my thoughts on it just being cosmetic seems to hold out for now. I will pick up some high temp paint to give the open metal a coat.
Also as a side note, since I setup fiber internets I didn't put the grill on my network yet. The app would have told me if it got to cold, or in this case too hot. So adding the grill to the network is another task.