Much more can be said about this, because I'm not sure we have a good answer on AH for what Christians thought about Islam in the 1st century AH/the 6th-7th centuries AD, but until then there are a couple of answers about what Christians thought a few hundred years later:

u/sunagainstgold wrote about I'm a Christian in the middle ages, and the Pope has just called for a crusade to take back the holy land. How much do I know about the Islamic faith of the people I'm about to go battle?

And I answered something similar as well: I'm a Crusader heading towards the Holy Land in 1096. How much do I understand about Islam?