Hi Wooba, your simple and clear "No" is a great response! I agree there's no need to explain--especially since it makes the interaction more complicated, and he didn't ask for an explanation. You accepted his gift of food, presumably thanked him, didn't stop him from joining family activities, and complimented last week's food when asked. This sounds like a positive, low-pressure interaction--and one that didn't send you spinning!
The "No" leaves it to him to explain the situation to his mom (a natural consequence), and he had the (no-need-to-point-out) alternative of attempting to patch things up with you if he had preferred.
