The community wiki flag is set automatically once a question reaches 15 answers: this is to encourage collaboration on existing answers, as after 15 or so of them, it's highly likely answers are going to overlap.
Unfortunately, this automatic action is marked with a confusing message: the person who had the privilege of posting the answer that triggered the automatic conversion to community wiki is the one who gets the attribution.
Our sister meta site, Meta Stack Overflow, has more background on the mechanics of community wiki, but you can rest assured that nobody has the ability to "troll" people with community wiki flags:
- Questions can only be converted to community wiki by diamond moderators or through automatic conversion
- Answers can only be converted to community wiki by the post owner, diamond moderators, or through automatic conversion