It's more complicated than that

Western philosophy of war is derived from the Geneva school. The Geneva Conventions work on the assumption that there is a clear and permanent distinction between civilians and combatants. Bush's unclear position re the Gitmo prisoners is a direct implicit recognition that this binomial distinction is utopian, for the first time in more than a century in the West.

Islamic philosophy of war (and non-mainstream Western philosophies of war, too, mainly but not only left anarchist / leninist ones) is more complex and nuanced. The distinction between civilian and combatant still exists, but is never as idealistically clear as it is in Geneva. In the extreme, combining this more complex view of the dichotomy with the rather strict exclusivism of Wahhabi Islam, you can end up with a philosophy of war that allows for acts that would normally be considered as terrorism.

Notice also that, even under Geneva definitions, there have been recent acts of war by Western armies which might qualify as terrorism because of their indiscriminate character. But that is another issue.