I'm not sure when the concept of an "Abrahamic religion" was developed, but medieval Christians certainly did not think of religions that way. They only had the categories of Christian, Jewish, pagan, and heretic, so Islam had to fit into one of those, and it was usually considered either a kind of paganism or a Christian heresy. I have a few previous answers to similar questions that will hopefully be helpful:

I'm a Crusader heading towards the Holy Land in 1096. How much do I understand about Islam?

as well as how some Christians had a slightly better understanding of Islam after the crusades began

and Why and when did Westerners stop referring to Muslims as Mohammedans?