It was not being stupid, exactly.

It was being efficient in the way brains are built to be efficient, which is to say it was pattern-matching, taking a small set of visual features, white powder, small bags, coded labels, quantity, and instantly retrieving the category those features most commonly belong to in the world of stories we are all steeped in.

That is a useful ability, most of the time.

It is how you recognize a face in a crowd or a threat in a dark parking lot, this rapid leap from a few features to a whole conclusion.