Considering that it is an honest answer, then yes, Atticus's explanation is suitable. The children know their father for his frank and open approach to things, unpleasant or not. Atticus is not in the habit of evading difficult issues and will, in a direct manner, admonish and inform his children about the realities of life. This approach can be seen in the various instances when he disciplined them and when he gave them advice. He has adopted a parenting style in which he desires only the best outcomes for his children, and he has been teaching them the values of honesty, integrity, and respect. In the process, he has earned both Jem's and Scout's admiration and respect.
The fact that Atticus deliberately couches his response in legal jargon would, of course, make it difficult for Scout to comprehend, which probably explains why she reacts in the manner she does. However, the question is not whether Scout understands it. Furthermore, Atticus knows that his daughter is intelligent enough to know not to pursue the issue any further. Being the character she is, Scout will not want to seem stupid, and therefore she accepts his response.
When Scout asked her the same question, Calpurnia realized that it would be awkward to explain. She knew that Atticus would come up with a more appropriate response and referred Scout to her father. Atticus, of course, does so with aplomb by answering another uncomfortably complicated question in the same dry manner that has become his custom.