The Capture of Antioch (Rudith Séva)

The excerpt below describes the capture of the city of Antioch (today a Turkish city) by the crusaders during the First Crusade.

“After the siege had been going on for a long time, the Franj made a deal with one of the men who were responsible for the towers. He was an armor-maker called Ruzbih whom they bribed. […] The Franj sealed their pact with the armor-maker, God curse him ! And made their way to the water gate. They opened it and entered the city. Another gang of them climbed the tower with ropes. At dawn, when more than 500 of them were in the city, and the defenders were worn out after the night watch, they sounded their trumpets… This happened in 491.”

Ibn al-Athir, Account of the First Crusade

Vocabulary

Armor (US) or armour (UK): metal clothing that soldiers wore to protect their body while fighting
To bribe: to influence by gifts, to corrupt
To curse: to damn, to use a magic word or phrase against somebody in order to harm them
To be worn out: to be exhausted, to be very tired

Questions

Were the Franks Christian or Muslim? Was the armor-maker an Arab?
According to this account, how were the crusaders able to capture Antioch?
Why does the author curse Ruzbih?
According to Western historians, the Franks captured Antioch in 1098. Why did al-Athir give the date of the event as 491?
Do you consider this account a reliable source of information about the crusades? Why or why not?