A couple of things:
It's not unusual to buy major stocks as they're falling because you know they're going to go back up. That's just common sense and any legit financial advisor will tell you so.
Agreed. The issue is rather than picking tariff resistant stock (like local energy companies, commodities, etc), picking companies that were expected to be incredibly impacted by tariffs (and whose stocks dropped because of this) and then those exact companies happen to be in the very narrow tariff-exempt categories to be announced immediately afterwards, especially when said person has not ever previously invested in these specific companies. That's a bit of a stretch.
As an example, if Trump said "We will put 100% tariffs on all imported fruits and vegetables!" and companies that rely on these imports all tank, then you buy dole pineapple stock, and afterwards Trump says "except for Pineapples. Because I like Piña Coladas". That's going to be suspicious.