The first reason being that the man looked exactly like Father and seemed to know about his family. Which would have scared him, at first, if it wasn't for getting the name "Hohenhiem" and remembering it from his siblings. Someone from a very long time ago, who knew Father before any of them, but...wasn't a homunculus...or human. Not according to his Big Brother at least. The second reason was with how quiet his head was. The Boy in Red was standing off...somewhere, Pride could feel his eyes even if they weren't there, but he was unusually quiet and still out of sight.
He wasn't brave enough to try and look for where the boy was, didn't want to have that conversation. Wasn't supposed to anyways. Instead there was a tilt to his head and a slight frown from where he was perched on the fire escape, looking down at the man who spotted him, "............try?" he asked, finally actually speaking.
Hohenheim stood silently in thought for a moment as he looked at the young blonde haired man on the fire escape. He looked a great deal like his son, Edward, but was it truly him? “I’m trying to understand something.” Hohenheim’s eyes took in the tattoos, the Homunculus tattoo he had noticed right away. Was this ‘Edward’ a mere clone of his son, just as Father was a clone of himself? Or was there something else at play?
“Tell me, what is your name?” Hohenheim asked as he took a few steps closer to get a better look at him. In a way it was truly remarkable and in another it was absolutely terrifying to think that something may have happened to Edward... after everything. “And... how were you made?”