The Islamic world was superior in technology in the age of the Crusades up until the Mamluks taking over Egypt. One of their leaders (I don’t recall the name) ordered the destruction of the rebuilt Library of Alexandria, saying that since the Koran was the word of God, and since all other books were either to reinforce that, or blasphemous, no other books were needed.
It was at that point Arab society lost its technological advantages and began to leech off the technological capabilities of the infidels, until this day.
No, the Arabs were leaching off the Hellenic tradition that built the Library at Alexandria. The Library at Alexandria was there well before the Arabs came.
I don't know think the Arabs ever had a technological edge. Certainly in the early crusades, the heavy western cavalry had a definite technological edge, commonly winning over greatly superior numbers. They just couldn't be supplied in the numbers required.
Battles like Manzikert seem to be more about tactics, strategy, generalship and politics than about a scimitar being better than a broadsword.
Actually, Arabia bit the dirt politically and culturally when the Mongols invaded and took over the place. The Mongols didn’t quite make it to France so Western Europe was allowed to “develop” itself out of the Dark Ages
However, most historians debunk this as the cause of the destruction of the library. They believe it was a combination of fires which started with Caesars assault on Alexandria and continued throughout the years. This, combined with the fact that the “books” were actually scrolls which didn't age well, led to the loss of the library contents.
http://www.bede.org.uk/library.htm
I believe that the basis of loss of knowledge and tech capabilities comes down to the same reason that Omar ordered the books destroyed in the story you spoke of. If it's not in the Koran and Mohammed didn't sanction it, Muslims can't explore it or involve themselves with it.
Pretty limiting in the scientific arena, eh?