Its more than that. It has to do with how words change in usage over time. Also because the book Dracula is so famous and Bram Stoker mixed the two myths together in his novel. He got a lot of information from Baring-Gould's book on Werewolves. There are other examples but this is one in particular. Most of it is just how superstition culturally evolved.
Here is an excerpt from one of my articles:
Even though Romanians use this term, “the word vârcolac is a loan from Slavic (cf. Bulgarian vǎlkolak, Serbian vukodlak), originally meaning "werewolf" (etymologically "Wolf's Fur"). However, the term has come to denote mostly vampires in Balkan Slavic folklore. Nevertheless, the idea that the vârkolak is a wolf that swallows the sun and the moon is also attested in North-Western Bulgaria. The pricolici is another form of vârcolac, also resembling a werewolf.”1
“A vǎrkolak (Bulgarian върколак) or vǎlkolak is an undead revenant or monster in Bulgarian folklore. Its name is derived from a common Slavic term, which means were-wolf in most Slavic languages as well as in modern literary Bulgarian, and is originally a compound of вълк /vǎlk, "wolf"/ and длака /dlaka, "fur"/. Nevertheless, the creature as described in original folklore is more similar to a vampire.”3 The reason for this is because it can be denoting any creature that is “wolf-like.”
Sometimes the word Vrykolakas or Vorvolakas is used interchangeable to mean were-wolf or vampire. This Greek word means someone undead but it really isn’t specific. Nowadays it has been equated more with the vampire even though it wasn’t exactly that in the beginning. They are not known to actually drink blood. Even though the original words meant were-wolf somehow the legends of the vampire and the were-wolf have gotten crossed as the word literally means “wolf fur” in most languages of the area.
The Greeks believed that it was actually after death that one would become a Vrykolakas. Usually they were describe as being someone who was heretical in life and perhaps had been excommunicated or ate the meat left behind by a were-wolf or was wounded by one. Some even believed after a were-wolf had been killed they could then return as a powerful vampire. They are said to be killed by being struck by a bolt of lightning or consumed by fire. It appears that some of the confusion may be due to works of fiction and perhaps Hollywood because even a Greek hearing this word might envision Dracula rather than the root meaning of the word.
Here is an excerpt from an account remembered by a Greek immigrant to the United States in 1934, concerning the nature of the Vrykolakas:
“The vrykolakas is the devil. The people hear about him in church and are afraid. No, I never heard of a vrykolakas drinking blood. These tempters (paraphrase for devils), whom people call vrykolakes, kill people. That's why people fear them. When they said to us that in such and such a place a stoechoio comes out, whew! we would never go that way; we feared those beings.
My father would see these beings when he walked at night with my mother; my mother saw nothing.
He looks like a man, like a dog, like anything. He comes out at night. When people die of a contagious disease, and no one will go near them and they bury them without a priest, without anything, they become vrykolakes.”7
There appear to be parallels between the legends of the vampire and those of the were-wolf. Most cultures believe that people can transform into other than human form if not physically through dreams or out of body experiences. Most societies believe the soul lives on and in some they believe that animals have souls. There is every likelihood to believe that the soul of a wolf or for that matter many animals could either share a body or inhabit one for a lifetime.
