Just wondering, can someone explain this to me?
1 Answer
There are some cases where user removal (account deletion) includes invalidation of their voting history and causes all users who received votes from that person to have their reputation changed to reflect that. This works in both directions, so if you had many upvotes from this person, you will lose reputation, but if you had many downvotes, you'll gain it.
If you visit your voting history (click on "user was removed" in the achievements list), you'll see a link to "learn more", which will take you to this page, which goes into a bit more detail than I have.