Why is the subjunctive mood used in this sentence?

"Flesh," said the boy, and he pronounced the word with slow relish, as though he were tasting it.

I was analyzing this sentence with my high school class, and one student pointed out that "he were" should be "he was." I didn't know how to respond to the student, but I have since discovered that the subjunctive mood is being used.

Are there any ideas at to why the author would be using subjunctive mood in this case?