Long ago, when disease porphyria came out people saw (victim) person with symptom porphyria, people were thought that person is dead with ugly skin and teeth and bald or with less hair on night, people were scared out of "vampire" with porphyria.
People killed innocent person, they wrote about vampire how person was killed with stake, or sunburn.
Person with porphyria, when person eat something his or her meat and/or muscles make teeth widely but not teeth goes down or canines just meat and/or muscles.
That's how legends of vampirism made.
In my opinion about Xavier's hematophagy not sure, on news still telling us about mutilation animals and UFOs.
Nowadays, UFOs never had mind with animals, just fake by Stalin's idea for Aliens to scare Americans and everyone.
About mutilation animals, I'm not sure. My theory hematophagians exists or just fake about mutilation animals.
Hope it's very informative.