My answer was converted to Community Wiki. Can someone give me an explanation for this?
It's because you edited your answer more than 8 times. According to the revision history, which is the link just above your name, at the bottom-right corner of your answer, you edited it 12 times.
Note that this feature has since been removed and editing a question or an answer can no longer convert it to Community Wiki. For more in-depth information about the Community Wiki feature, please see the FAQ.