Hello! This is an example given for a partitive article:

Tu veux des pommes de terre?
Do you want some potatoes?

My question: is “des” both a plural of the partitive articles (used with uncountable or mass nouns)  AND  a plural of the indefinite article (used with countable nouns)? In the example above, potatoes are countable so they would take the definite or indefinite articles. But the sentence is used as an example of the partitive.

It’s probably a stupid or obvious question but I’m confused!

Thank you!