Totally normal..when they shed they shed a small amount of skin just inside the vent. This tissue is very thin and has capillaries close to the surface. as a result some time a little tear or stretch in the tissue may happen resulting in a slight amount of blood loss. It can happen when an animal is Popped or probed incorrectly, to aggressively or by an inexperienced person.
I see it allot in animals that have humidity issues or are aggressive/really active when they shed.
Small amount is OK ....Big ole soaked area not so much.