You know how school get your exams early, like your actual AS exams delivered early?
So one school in my area opened them to do the mocks for their year 12s because they decided they weren't going to submit the paper for marking, and the year 12s realised in was the actual 2016 OCR science paper, and so they told all their friends at my school what was on the paper.
So basically some people saw their AS papers before sitting them, and they all got As.