Even with the huge explosion, Ibuki was still standing there unscathed. They're not even tiny scars or injuries. Ibuki didn't even feel any pain or damage because of that explosion. He then began to laugh again and mocked Oldham that his attacks were weak.
Oldham was surprised to see Ibuki was unharmed even after taking that explosion. He then realized something weird about Ibuki. Oldham looks closely at Ibuki and he saw something around him. An aura that he was familiar with, a demon god aura.
"You aren't a normal undead..."
"Sadly I'm not...but the same can be said for you. You aren't just a human."
"HAHA! This man is nearly my vessel to greet you, my real body was elsewhere."
Ibuki now knows why this man has a godly vibe in his voice, Oldham was already dead by the strike he landed before. There is someone else using Oldham's body and continuing the fight with Ibuki.