i'll keep it short and simple (since I don't have much time and there are probably way more qualified people to answer it thoroughly.

• That comment is wrong. Persia had accomplished way more than Arabs before Prophet Muhammad. After Persia was conquered by Arabs, they continued to contribute to science/math/religion etc. in fact, Ibn Khaldun (an arab) suggests, it is a remarkable fact that with few exceptions, most Muslim scholars…in the intellectual sciences have been Persians. One last quote from an Umayyad caliph, an arab called Sulayman ibn Abd al-Malik, who said

The Persians ruled for a thousand years and did not need us Arabs even for a day. We have been ruling them for one or two centuries and cannot do without them for an hour.

I'm not saying Persians did everything and Arabs didn't. I'm just saying Persian did way more than what that comment wants you to believe.

• To answer your (direct) question: Arabs burned alot of the books and documents that they considered went against their belief, even if it didn't necessary do that in the eyes of others. This is just one of the reasons, not the only one.

If there is anything wrong with this answer, I sure wouldn't mind being corrected :)