It could be that the person has a very strange and unorthodox way of looking at the Harry Potter universe. They might have focused too much on some of the more mysterious or less - explored aspects of the magic in the series and then twisted it into this 'evil god' idea. However, the main storylines clearly don't support such a view. The series is about the struggle between the good wizards and the dark forces led by Voldemort, not about an 'evil god'. For example, the use of the Unforgivable Curses in the story is a part of the dark side of magic, but it is used to show how evil the Death Eaters are, not to promote an 'evil god' concept.
Maybe it's just a really out - there and misinformed idea. Some people might be so used to mashing up different concepts in their minds that they make this odd connection, but it has no basis in fact.
It could be that they have a very different understanding of what 'Harry Potter' is. Maybe they are confusing it with some unlicensed or poorly made fan - created works that they wrongly assume are part of the official 'Harry Potter' universe. Also, some people might have a very narrow view of what is considered proper literature and wrongly label it as 'delinquent' without really understanding its value.
It could be that they've seen some really out - there fan theories or crossovers that made them misinterpret things. Some people like to create wild combinations of different fictional elements, and this might have led them to this strange idea. However, in reality, the two are completely separate entities with their own identities and storylines.
Well, maybe someone who doesn't really understand the essence of either could make such a strange claim. They might be confusing the elements of magic in both concepts. But really, it's a very far - fetched idea.
Well, it might be a very strange and misinformed idea. Maybe someone who doesn't really understand either franchise very well just made a wild connection in their head. But as we know, Harry Potter is about magic and wizards, and Sonic is about a speedy hedgehog. There's no logical basis for such a claim.
They might be very confused. Maybe they haven't actually read either the Harry Potter books or Greek goddess fanfiction properly.
It could be due to a misinterpretation of some common elements that they think are shared but are actually not. For example, both series have characters with special powers. But the nature of those powers is completely different. In Harry Potter, magic is more about spells and potions, while in Naruto, the Uchiha's power like the Sharingan is a ninja - related ability. People who don't fully understand these differences might wrongly think Harry Potter is an Uchiha fanfiction.
Maybe someone who is very creative and looks at the broad concept of magic in both. They could see the heroic aspects of Harry Potter and compare them to Arthur Pendragon's heroism. But really, it's a stretch. Harry Potter has a very different set of rules for magic and a different kind of society compared to the Arthurian world.
Maybe they are completely misinformed. They might have heard some wrong rumors or got confused with some other works that might have some loose connection to Bermuda but are not related to 'Harry Potter' at all.
I can't really think of any valid reason. It might be a completely misinformed idea. Maybe someone who is not very familiar with either Harry Potter or Vergil's works just made a wild and incorrect assumption. But in reality, there is no connection between them in terms of story, theme, or origin.