It's worse than that - from how I see it, it was all very deliberate, and somewhat clever.
1) How will the market response if we suddenly suspend the tariffs for 90 days?
2) Let's find out - create a 'rumor' that that has happened, and retract it a few hours later.
3) Boom! Stock market goes straight up. Make notes as to what parts went up the most.
4) Let everything settle back down again.
5) We need a 'trigger' - something that tells us when to start buying beforehand. The Trump post is perfect for that. Not too subtle, but provides some kind of plausible excuse for doing the pre-buying. And even a plausible excuse for *what* to buy based on what the market did when the rumor came out.
6) A few hours after the trigger, make the official announcement and the market is off to the races.
7) Solid grift. No way Trump came up with this on his own either. Everyone knows you did it, and see it being done. But can any of it be proved? And like you pointed out, is there anyone left to try and prove it too?