I think the article tried to refer to this link https://arxiv.org/abs/2504.10663 As I understand from scanning the paper, the authors attempt to determine differences between the Russian wikipedia articles and the articles on the Russian fork. They show that articles on the fork that were that differ from RU wikipedia have a significantly higher number of edits on RU wikipedia. The authors suggest that these may be signs of manipulations, however, it may not have affected the quality negatively (as stated in the discussion).

I do not find state sponsored activity on Wikipedia unlikely, but I am not convinced there is clear evidence that Russia poisoned wikipedia succesfully.

Wikipedia is full of state-sponsored activity, and even fuller of useful idiots for those states. Russia might not be doing it in particular, though.