It is referring to a recent literature review. I've read several versions of the review and discussed it with someone close to the process. It's a review, so not any new study. It just looks (and does so rather imperfectly) at the available literature and existing studies.
In a nutshell, the review observes that there is little evidence to suggest that any kind of kava can in itself be seen as clearly toxic to the liver and that there are some questions regarding the quantitative thresholds used for differentiating between cultivar groups. However, the report does not claim there are no differences between cultivar groups and it does not suggest that all forms of kava (extracts, beverage, raw powder, fresh etc) are the same and have the same safety profile.
Overall, no new findings, but just an attempt at summing up the existing scholarship. In some aspects it's an OK review, in others it fails to engage important literature and/or overlooks more nuanced, albeit quite important, arguments.