I've been reading all over the site to find the answer but can't find it. I don't see what I did to earn it, but thanks anyhow!
It says: "Reputation gained on this tag..." when I hover over the tag "user-account" listed in my Reputation Tab.
when I hover over the tag "user-account" listed in my Reputation Tab.
I presume you are talking about hovering here?
Your top tag is user-accounts so it is showing you the rep you have gained from questions (and answers if you had any) that contain this tag.
It is your top tag because you have asked two questions with that tag. All the other tags appear in only one question.
You can earn badges for tag reputation:
Ignore the green ticks - they are displayed because I have many of these badges.
I think you're talking about this thing in the Reputation section of the Activity page (I'm mousing over the
Just participating in the tag didn't give you rep; it's telling you how much rep you got because of good posts you made with that tag. Those points were already included in your total rep.
The original content of this answer follows.
To be honest, I'm not sure what you mean. You can earn rep from edits to tag wikis and by edits to other people's normal posts (which could involve retagging), but from your public reputation history, it doesn't look like either of those things happened. Here's what I can see:
Interestingly, your first question no longer has an accepted answer. I don't know whether you unaccepted it, or whether the accepted answer was deleted for reasons of moderation (e.g. via Low Quality Posts review). I was under the impression that the +2 you got for accepting an answer is automatically taken away when the question stops being accepted, but that does not seem to have happened here. I suspect those two points may vanish somtime in the future, or the next time you visit https://superuser.com/reputation.
I think that accounts for the two points not associated with a post in your rep history.