When I was writting that, I assumed it was about the party, so clearly not so unambiguous. It could conceiveably refer to either - doubly so in casual speech where rules are bent. Fill up a books worth of text about a character using they/them pronouns (esspecially written by a bad writer) and you get confused often.

To be clear, in ideal English, its easy to use. Most English is not ideal, with words being changed, dropped, reordered, ect. based on the speaker or writer’s whim in the moment. All that is before factoring in regional varients of English.