You don't have any reason to tell me everything either, Giorno. [Less reason, in fact. Not that Dio will verbalize that here and now when it could perhaps reinforce the idea that he should withhold from Dio any further than what he's already said.] You're clever enough to know what I was doing and you could have lied to me just now if you wanted with very little I could do to prove otherwise.

I accepted that as a potential outcome, so it wasn't about affording you that chance. But I wasn't indirect for the sake of being coy or toying with you, and it wasn't purely for my sake either.

[Normally, Dio wouldn't bother to explain even this much. He'd leave it alone, leave it as a question in the other's head as to why Dio does the things that he does because it gets them to entertain a number of possibilities and either are wracked with indecision or gravitate towards what's most desirable. But that's not to his advantage right now. It's obvious even from the length of this conversation that the ideas Giorno now holds about his father are largely cast in the light of a villain, perhaps even something edging close if not completely within that of a monster. Furthermore, just as Giorno doesn't have a reason to tell Dio everything because it's likely he's still trying to determine how much he can trust his father. Questioning Dio's motives may sometimes grace the side of something a little more positive, but it's not likely where Giorno would invest as the most likely explanation and he'd see an extreme lack of any candor whatsoever as a reason to treat Dio with suspicion.]

[No, at this point, with Giorno knowing so little for himself beyond his mother's words and the images he created for himself, it's better to be at least vaguely transparent. Whether Giorno accepts it at all is entirely up to him, but Dio has laid it out for him all the same.]