The problem of stolen tweets has been here for a while. Someone tweets something phenomenal and/or original and rather than retweet it, certain notorious handles are known for copying it and tweeting the content as if it was their original thought. That is how tweets are stolen.
Well, Twitter is taking it serious now and will delete tweets stolen from you, if you file a legitimate complaint. For the complaint to be legitimate, you have to be a creative e.g. you are a writer, photographer or other creative. An example would be a professional writer who tweets excerpts from their book, and someone steals those tweets, that certainly qualifies. The full scope o=is not immediately clear.
If someone has stolen your original tweets and tweeted them as their thoughts, to have something done about it, submit your complaint on Twitter’s copyright infringement form.
You can read more about this here: Twitter is deleting stolen jokes on copyright grounds