The section "What happens when you submit a change" uses the term "tag" referring to the "t" option's argument. However, the git-review documentation refers to that argument as the "topic", which is consistent with how this concept is referred to in Gerrit.
Moreover, "tag" has another very common use in Git (viz, git-tag), which makes it even more confusing.
I'd like to propose to substitute "topic" for "tag" in that section.
This post was posted by Gnustavo~mediawikiwiki, but signed as Gnustavo.