This "easy way" will get you 0 out of 3.5 points if I am the grader. Saying essentially "the ingredients used fit the style because they fit the style" doesn't display any knowledge at all. I think it is terrible advice.
But at least the exam-taker addressed that portion of the question, which a lot of people don't. And, depending on the grader, you might get partial credit, so it's worth a try if you don't have anything else to say or if you don't have time to write anything else. It's not the best advice in the world, but it's not utterly useless.
The all-grain recipe question is one of the toughest and most time-consuming questions on the exam. There are a lot of places where, even if you know your stuff, you can make mistakes. And, if you're doing it right, you have to write an entire short essay on how to brew a particular beer, complete with recipe from grain to glass, in 10-15 minutes.
BJCP for Dummies at least gets you in the ballpark in terms of how you should answer the question and the sort of information that graders want to see. No, the techniques in the guide aren't going to get you a 10 out of 10 on the question, but they might get you a 6-7 out of 10 when you otherwise would have gotten a 3-5.
While studying to take the exam for the third time (second time I had a sinus infection and a bunch of wrong-headed ideas on how to game the exam), I made heavy use of BJCP for Dummies when creating my own exam and pestered senior judges on the BJCP member forums about what constituted a good answer to the various questions on the exam. I'm not sure how I did, but I'm cautiously optimistic. I finished the exam with time to spare and I think I did well enough to get a National score.
Because my results are pending, I can't say for certain if my efforts paid off, but I think that BJCP for Dummies was a useful starting point.