Who is the Community user?
I found this question shown on the "active" list, as in the following picture:
But I went though carefully on this page, none of the operations was done by "Community".
Is this a bug?
No, this is not a bug.
The Community user automatically bumps "old", unanswered questions to get them some attention.
This is confirmed by the "about me" section in the Community user's profile:
Hi, I'm not really a person.
I'm a background process that helps keep Stack Overflow clean!
I do things like
- Randomly poke old unanswered questions every hour so they get some attention
- Own community questions and answers so nobody gets unnecessary reputation from them
- Own downvotes on spam/evil posts that get permanently deleted