I mean, the article starts by explaining the fact CSS anchors was pushed as a chrome feature. Only browsers that inherit from it by default will have this.
The article doesn't mention that it's not supported by other browsers. The two things (pushed by chrome / unsupported by others) are not consequential.
If you don't clearly state it and people start using the shiny new thing you're hindering the few alternative browsers out there.
> This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.