Maybe Sylar walked in on the Haitian and Peter and just figured that Peter had brought a friend along for moral support? If I recall, the only time Sylar met the Haitian was in the middle of his mind being wiped, so, it could be Sylar figured he was the only person in the room with powers.
Or, y'know, the Haitian just hid behind a potted plant for the duration of the scene.
Or, y'know, the Haitian just hid behind a potted plant for the duration of the scene.