Well, of course we don't yet know if he bought it or if he's just acting like he did to fool Kabuto. But basically when Kabuto gives a speech like that, it's 100% assured there's at least a 50% chance he's just utilising an extremely cheap way to ensure he won't be one-shot killed right off the bat. Despite all of Sasuke's bravado and tough guy acting, I reckon he's still so "innocent" that he now imagines they absolutely must capture Kabuto alive.