That article doesn't really confirm anything. Just speculation from the author in the article.
From Yves' quote in that article: "the extra cost to put to make sure the games work well on Stadia is not that high". For all we know, Ubisoft's CEO might be talking about making sure the PC game work well and users have a good experience when the game runs with Google's Stadia streaming technology. Perhaps, adding support in the existing code for the PC version to play well with the Stadia platform.