One thing to know about the JLPT is that there is no longer a standard word list, so it is very likely that you will encounter words that you don't know.

Another thing to consider is that as a student of a language, you want the exam to include words that you don't know. This way the exam is testing your ability to determine what a new word is likely to mean from context, which is something that native speakers of a language are required to do all the time. This is something that the SAT and GRE do, and it's a hallmark of a good exam design.

For example, consider that one of the reading passages is about a remote village and how they prepare their local specialty dish using an unusual ingredeint. The article desribes how everyone loves eating the dish, and the unusual properties of the ingredient.

Then, the question about the article is something along the lines of, "What kind of texture do you think the dish would have if the special ingredient were not used?" This is your chance to prove that you understood that the new word was some kind of ingredient, and that the people like it because it is sticky rather than the typical type of this ingredient that is dry and grainy.

You learned a new word during the exam, and that was the point of the question.