I would rarely use the plural "yogurts" in English, even to mean "multiple little pots of yogurt," and not here to mean yogurt in general.
This is one of a number of situations where what is natural in French is not natural in English. Yes, the French are used to eating little containers of yogurt. In English, the plural form is normally lost in translation and it does nothing to insist on "yogurts" here. That is why the singular (or "mass noun") form is accepted.
"Ne... que" expresses a restriction or limitation, and it means "only".
- il ne mange que... = il mange seulement... = he only eats (some)...