Alas, in horror and supernatural fiction, there is more than one reason for eyes to glow red. The most immediate reason would be something like vampirism: if the eyes are red, run away. This is because blood is associated with vampires. Red eyes can be associated more generally with predators, such as werewolves, or with madness and possession. This is because red is associated with anger, with flames (like the fires of hell), with passion, and, always, with blood. It is also unnatural, and related to things that scare people, like rats, whose red eyes give some people the creeps.