How did this happen???? Is there some possibility someone else may have done it? Was it because of the editor I used? I'm just really terrified right now because I'm being accused of vandalism that I honestly don't remember doing.
A good way to avoid this is to always click "Show changes" before clicking Publish when editing a page. "Show changes" can be found under the little arrow next to the Preview button. This way you can review the changes you've made before publishing them.