Is this a rude question towards your server? And what entirely is it supposed to mean?
Automatic response is to think that a customer considers the restaurant serves small portions and have gone in with that assumption.
I would think that if you even have a question (but not to ask-just assume that portions are smaller and an added course may be in order) to the order courses to what you would think will fill you up-may it be a salad or app order.
Why ask? To me it just seems rude, and a complete insult to the restaurant. How is a server supposed to answer that type of question?