It wouldn't "distort" the results. It would enable you to get results at all. The number of likely uncontrolled results in this "experiment" means that it was worthless for anything other than getting children excited about science.
As said I agree that an "additional" test with a faraday cage should have been done, but not by the children. I expect the scientists to come up with that idea. Having too high expectations from children is counterproductive.
