How can you call her childish? Have you eaten? This simple greeting of meeting and talking has become our most common greeting. Doesn't mean it's normal to ask this question only at dinner time. In real life, I don't think this is dinner time. People are used to saying this simple greeting. Including me, I also use these four simple words to greet my friends when they are not eating. I don't think anyone will have your idea. People think it is normal to say such greetings at any time. Maybe this girl has nothing to say to you, and she will be nervous when talking to you. It's normal to be nervous when talking to someone you like, and then you will say the wrong thing. Maybe you don't know what this girl is thinking. Don't take it personally. I wish you happiness.