There's the didactic argument where they did it analytically but explained the intuition of the analysis mechanically. There's also the oversimplification argum

There's the didactic argument where they did it analytically but explained the intuition of the analysis mechanically. There's also the oversimplification argument where they actually did some kind of much larger sampling from a trained decision tree but then boiled the mechanism down to something easily understood by casual readers more interested in "Jeopardy!" than statistics.