When a user account gets deleted, some of its actions (votes, reviews, etc.) sometimes move to the Community account so they will not be nullified (sometimes we do want these to be nullified, in which case the Community user is not assuming ownership on these actions).
Sometimes it's easy to just leave some traces of who was that user. But sometimes it's just not how things work.
I wouldn't worry about it. It just means that someone reviewed this, but then their account was removed for one reason or another.