it's not really asking if you have eaten rice in general- unless the context of the conversation is very specifically about what carbs you have eaten (i.e I just had some bread, did you have rice or bread for lunch? kind of convo). But in this case the question will be rephrased. 밥 먹었어요? is mostly mostly saying "have you had a (proper) meal?" It's not just asking if you've eaten something. In a similar context, 밥 먹자! is like "let's grab a meal together" , not just let's snack together. 간식 is snacking in Korean.

밥 literally means "boiled rice" But, here 밥 means "food, meal" 밥 먹었어요? means "Have you eaten?"