Byakuya is proud, but I don't think he's stupid. I think he realized that Ichigo has grown more powerful, and the attack can be seen as actually a mark of respect. When they previously met he didn't want to attack Ichigo while he was distracted. This wasn't about honor, really, but more contempt of Ichigo's skills, saying that he didn't need an edge, because even fully prepared Ichigo wasn't close to a match for him. Now he takes that advanatage, because Ichigo's improved and he might actually need it. Either way, should be a good fight.