They don't know that... it's an anecdote, not an epidemiological study. But you also have no evidence that diets changed drastically for the whole city of 500k

They don't know that... it's an anecdote, not an epidemiological study. But you also have no evidence that diets changed drastically for the whole city of 500k people around the same time... Probably because we don't even know what city this is actually referring to. Maybe all 500,000 people all stopped brushing their teeth... Maybe all the dentists left town... Maybe aliens are dosing the town from orbit with radiation weapons. It's not a useful counter-point for you to just assert some alternative causation... Of course there could be other causes, that's literally always true about any causative assertion.