There are some answers or questions edited by the @community user. I think, this is a bot, but if you look at this answer https://matheducators.stackexchange.com/a/1381/114 and its revision, @community acts very human. Can someone explain it to me?
Even persons not having an account (not even and unregistered one) on the site can suggest edits, via "improve this" below a post.
These suggested edits are then "owned" by the Community user; if/when the are approved it looks as if the Community user edited the post.
In the revision history of the post you can see that it is a suggested edit, as it says "suggested by." When you click on the suggested you get further details and can see that it was suggested by Anonymous.
Generally speaking, the Community user gets everything that needs a user that "owns" it but does not have one (anymore). Mainly, this is visible for suggested edits, but there are some more corner-cases, e.g., if user A votes to close post P, the account user A gets delted, and then the post P gets closed (in this order!), then Community user will show up in the list of closers (as the vote, technically/internally I think it is a flag, from User A got transferred to Community on deletion).