I think what little we do know about the research also exposes flaws. For example, although the BBC prompted the AI to only use BBC sources, it admits that other sources were used to compile responses. But the BBC only judged the accuracy of the answers against its own reporting. So, the AI summaries might well have contained info that wasn't in the BBC reports, but it may have gleaned those from other sources.
It would be interesting to see the experiment repeated, but with the BBC feeding the AI PDFs/text of the initial reports. I suspect it would be much more accurate.