Since the goal and objective of the islamists (i.e., radical mohammedans who believe in holy war) is to spread islam and make it the dominant movement on the planet (and virtually all of the islamists are in lock step with that) the conflict they have started is definitely a religious war. If Catholics started a conflict to spread Catholicism worldwide via terror and violence, and their main target were Buddhists, and the Protestants were opposed to the conflict, but said and did nothing, that conflict would still be a religious war, wouldn't it?
As you say, 'virtually all', that's not all, or, in this case, probably not even the majority. Only if ALL, the Catholics, including the Pope, were involved in the conflict, and only if Buddhists, were the only ones targeted. This is not the case currently.