I don't know if I've made it clear, but Clark's only contact with Kryptonite before this episode was in Smallville, when Trask was there. The piece that Irig sent to the Wichita lab disappeared, and Clark had no reason to think that Luthor would have any Kryptonite. *We* know that Luthor got hold of it because we saw "Barbarians at the Planet", but Clark really didn't realize there was any reason to worry.
Nan
