Branches are expected to change, tags are not. Tags are also mildly harder to change. A tag seems more apt for an archived branch. So I sort of see where OP comes from.
Yeah. But WHY taging instead of renaming the branch ?
I don't say if it is a good or bad idea. But I would like to know why.
If you read the article, it credits a reddit thread as the source of inspiration; the thread ultimately points to a StackOverflow answer [0] which may offer a better argument as to why they liked yo use this pattern.