St. Thomas, while justly respected as a theologian, doesn't define dogma for the Church. Also, the passage you cite says nothing about Islam at all.
In any case, your observation is irrelevant to my point, which is that indulgencing a crusade against someone does not contradict the idea that that someone worships the God of Abraham.
If I had read further before posting to you about not understanding your point, I would have saved bandwidth! Sorry, ignore the question above!