It's the original source material - in the Vampire Diaries verse, being a werewolf is hereditary, but they only trigger their curse by causing someone's death, so those characters had the choice to ensure they never did that so they never had to turn. If enough generations of them made that choice, it was possible for someone to not even know they carried the gene.

It wasn't always that simple - the character this one is about always knew his father was going to force him to turn one day, while one of his friends, who had grown up in foster care and didn't know who his birth parents were at the time, had no clue until he accidentally triggered his. Only two are known to have lost their curse. But to some extent a lot of them did have some choice.