It's communicated by context cues the same way one word has different meanings and context points to towards the meaning the person is communicating with a word

Though it does get annoying when the context cues are missing for example someone asking you if you want chips and not specifying what type

I'm guessing Australian language for "chips" calls them both that because they are a product made from potato that is usually salted and the two in the image are just different styles of the same potato product