It looks like the answer has now actually been deleted, and converted into a comment under the question, so you would appear to have been correct in flagging it as a link-only answer. So, it would seem that this issue is now mute.
However, as to why your flag was declined, only the decliner would know that.
Nevertheless, for historical purposes, it might be worth trying to find an archived version of the page to which the link referred (using the way back machine, maybe), and posting a new answer with both the wayback link and the relevant contents of that said page.
This more up to date version of (presumably) the same page, Format existing text as vertical text, is for Visio 2021, and may not be applicable to Visio 2007.