I think it's the hollywood 'a little scar makes me disfigured, I cant get married' type deal. They obviously don't want to make the visual representation of the mc truly ugly since many people will drop it, so they basically draw a normal mc and call him ugly. I suppose we're supposed to imagine he's a ugly guy.
@Geohie I don't think so. Who called him ugly? The Goddess. How do her humans look like? Like movie stars. So in comparison, his average looks is ugly in that world.
Yeah you're right. I thought his nickname of 'Hero' in school was because he was ugly but realized that it was actually because he was absolutely average looking while being among hotties.