Yea seriously, I feel like youtube should have some kind of test/study before it lets you become a monetized partner. I keep seeing the same misinformation/confusion/wellisawhimdoitwhycantiWTF kind of questions quite often.
That doesn't mean much. It's possible that whoever reuploaded it has permission or more likely uploaded and got hit with a content id claim (ads show up, but its the claimants ads and not the users). Either way no, you can't usually monetize trailers unless you have permission or doing some indepth analysis (and even then its not a guarantee)