If they bought the DRAM in order to stop their competitors from using it because they are falling behind, that's anticompetitive in spirit, though I'm not sure if it actually breaks any laws.
Before you buy anything from a store, do you also show them all your receipts from the other stores you visited today?
That's exactly the goal, to raise prices for OpenAI's competitors.
There is no reason to pathologize or find suspicious these normal economic facts. Especially when it is not within the power of a big player to choose how other people react to their actions, which is all "moving markets" is. If something is suspicious and illegal about that, then it is equally suspicious that you and I seem to go along with this "market movement" by these big players and pay the new prices. Are we colluding with them? We could do with less conspiracy-minded interpretations of these things.