Both the question of Student 1 and the answer of Student 2 are considered "stupid". The question sounds silly because by definition, the crusades were religious wars:
(also Crusade) one of the religious wars (= crusades) fought by Christians, mostly against Muslims in Palestine, in the 11th, 12th, 13th, and 17th centuries (source)
The concept of the Crusades is widely known in Western civilisation (and is taught in high school) which makes it odd for a college student to be completely oblivious to the fact that these wars were all about religion, more specifically christianity (Catholicism).
Now, about the pope: students are taught (again, in high school) that the Pope is the leader of the Catholic Church. There has always been a pope ever since the year 30. The first Crusade started in the Middle Ages, in 1096 to be exact. Again here, a student in college is expected to know that the concept of a Pope has existed since the birth of the Catholic Church at the beginning of the first century. Furthermore, they should know that the Middle Ages, during which the Crusades took place, is the historic period that lasted from the 5th to the 15th century, more than a thousand years after papacy had already come into play. The fact that these two students seem to lack knowledge of these historical subjects makes them sound "stupid".
Also, a Pope is not "invented". The word invented is one that you use for machinery or technological things, not for a person; a Pope is elected. Again, this poor word choice makes the student sound "stupid".
In Western countries, and especially Europe and the USA, anyone who has attended high school is expected to know all of this. These two students are in college, which means they have already finished high school. The fact that they do not possess basic knowledge of Western history is considered to be, to use a strong word, ridiculous. That in turn makes it funny and worth posting on a website as the one you linked.