Offering food expresses generosity and respect, but guests do not all have the same circumstances. Bilal answered “I am fasting”: he neither insulted the invitation nor concealed his situation.
الْغَدَاءَ يَا بِلَالُ is a concise invitation to the meal. يَا بِلَالُ is an address by name. Hospitality should allow a guest to explain a reasonable difficulty without embarrassment.
For example, a guest may be observing a voluntary fast or unable to eat for a legitimate reason. The host should not treat a polite explanation as rejection; the guest should respond courteously.