From screenshots I've seen from some users this has happened to, the "Delete this Tweet" button they offer you in those circumstances comes with a statement att

From screenshots I've seen from some users this has happened to, the "Delete this Tweet" button they offer you in those circumstances comes with a statement attached saying something to the effect of (paraphrased, but not too far off from the actual text) "Deleting this tweet amounts to an admission that it violates our terms of service" or somesuch similar, basically saying that they're incapable of mistakenly flagging a tweet.