[That's definitely something understandable to leave out, but as it is, it's obvious that a flash of terrified recognition has just run across Jonathan's face.]

H...How abhorrent of him! He sounds almost like...

[Yeah, that. He doesn't say the name directly, and he's not going to divulge too much information about Dio to a stranger. On top of that, he isn't entirely sure what an Archfiend is, but it doesn't sound like something that hangs around with puppies and fields of flowers.]

For what it is worth, I am truly sorry for your loss. I know it can be difficult, being the only person who survives time and again.