Yes, and he also posted a recommendation on Truth Social to buy stocks.

There's now indeed an "official" market manipulation accusation against Trump initiated by Senator Adam Schiff and others, see this article for example.

The alternative explanation is that the shift was part of the plan, but not with the goal of enriching themselves, but to pressure other governments to initiate negotiations to lower tariffs.

This is also the narrative the Trump government members (e.g. Karoline Leavitt) are now using to defend themselves. However: If you already know that you'll retract a measure and the market reaction is predictable, nobody would have used this information personally to profit? This is also quite naive ...