Theres two ways to manipulate the price of oil, you can cut back production thus increasing demand or you buy up all the production or as much as you can and sit on it creating the same demand. Which one are they being accused of?
The best I can tell from the story is that they think somebody might be “painting the tape” in thin end-of-day trading. I’d have to bet that that eventually points to speculators instead of producers and end users, as there are almost certainly many more speculators, and of course they were the ones who ran it to $140 a couple of years ago.