There is a setting in the “Reminders” app where Siri will automatically categorize your reminders into certain categories. If you have a shopping list and you add chickpeas and red beans for example it might put them into a category of “pulses and grains”. I think the idea is you probably buy all the things in a particular category from the same kind of store (or the same section of a supermarket or whatever).

For me yesterday I needed to buy dishwasher rinse aid so when I added it to my shopping list siri put it into the “beverages” category, and when my wife on a different occasion asked me to buy some makeup remover for her siri put that into a “condiments” section.

I have not done anything (on purpose) to make the classification like this by mistraining it or whatever - it’s just been that bad out of the box.