It's same weird like "the friends". Party is not a restaurant that serves food nor the person who owns the food. So normally at the party you can sometimes find some decent "comida" which is not obligatory though. Considering relation between words "la fiesta" and "the feast" i woud assume in Spain it might be different - learning language is about learning customs as well - one have to come with the other or it won't work. And "the friends" is something else as "friends". Saying "we are the friends" would rather sound like we are the actual guys playing the "Friends" or we are those famous friends everyone is talkinng about ..