Maybe that news was published 400ms or even a little bit earlier. Such little difference human beings cannot notice. Those who trade early were those who utilized A.I. systems to watch and analyze the report and trade accordingly, 400ms is long enough for big expensive machines to accomplish that task. To add even more conspiracy into the story, you can imagine someone was paid to publish the report just about 400ms earlier than supposed to by those who use computers to trade, and not very many people will notice, or just like post said feds don't even think this matters.