Sith or not, this one certainly had a dark influence. Otherwise his lightsaber wouldn't be that color, and Obi-Wan could feel the anger rolling off of him. Apparently he'd hit a sore spot.

His brows then rose at the boy's declaration. "Oh really? And why would that be?"

Though the Jedi isn't doing a very good job at hiding the expression on his face, suggesting that he isn't convinced that the lightsaber is working as it should.