Charlie
the piece of matza had fallen into the pot (not in a dish). I assume it was the kli rishon cooking on the fire.
Those who have a minhag to avoid, do not eat in a pot used for gebrokts. There is not a real halachic concern about flour that did not mix properly, because even if there were, it was baked along with the matza, and we are taught such baked flour does not create chometz (although it’s rabbinically forbidden to deliberately mix baked flour with water). But yet those who avoid, can’t eat (for the 7 days) in a pot used for gebrokts. So the shaila (of course it is a question about a specific minhag, not about halacha) is if the food can be eaten and possibly there is also a question if the pot can still be used e.g. the next day (when it would be deliberate and not accidental). I don’t think it is a trivial question.