It’s not even entirely a matter of if what he said can be disproven in this case, because he didn’t even reference a specific stock.
Speculating that the general market will go down, even if you use lies to say so, doesn’t count as stock manipulation.
And even if he had singled out a specific stock, speculating on what would happen if an administration with opposing political views comes into office is not the same as saying, for instance, “the CEO of this company actually just stole 20 million bucks and it’s gonna tank valuations” while shorting the stock.