Shiloh took that to be a 'no,' because he assumed that someone comfortable with sex wouldn't be so embarrassed by it. He didn't know it was a standard reaction for teenagers when discussing sex with elders - see, Shiloh considered himself the adult in their relationship, much older than Aaron was.
"You haven't. Have you thought that a condom might make it easier not to be," he thought, paused, "overwhelmed?"