Firstly, 'creating' a tag and creating the tag's Wiki and Excerpt are separate processes. From my answer on the link Vemonus linked above:
- The person who first uses the tag is the person who 'created' it - either by asking a question with it, or by editing it onto a question (with some caveats to do with deletion, merging and renaming tags).
- There is a difference between creating a tag (i.e. using it on a question for the first time), and creating the tag wiki/excerpt (the informational pieces of the tag).
As to Community 'owning' the creation of the Tag Wiki: this happens whenever someone under 20k reputation suggests an edit to a Tag Wiki.
My guess is, Tag Wikis and Excerpts do not automatically exist in Stack Exchange's databases when a tag is created. I'm not privvy as to why, but I speculate it has to do with not wanting to insert blank rows into the DBs for performance and storage reasons (especially as extraneous tags can be deleted off of questions with relative ease).
However, once you suggest an edit to the Tag Wiki, it needs something previous to compare against for the purposes of the review/edit system. Thus, 'Community' creates a blank tag wiki and excerpt, so that your suggested edit is displayed as a 'revision' correctly.
If you take a look at the Community user, you can see it's just a bot account that handles a variety of functions:
Hi, I'm not really a person.
I'm a background process that helps keep this site 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
- Own suggested edits from anonymous users
- Remove abandoned questions