tl;dw: the "juice" Schneier refers to is essentially the correlation between a bunch of static array bounds in the Stuxnet code, the layout of Natanz' enrichment process as computed by a respected American nuclear physicist in a public paper (based on data from an intentional leak by the previous head of the Iranian nuclear program), and finally hard evidence of this layout in SCADA screenshots from the plant that were released by the Iranian government.

This summary makes the correlation sound almost coincidental, however the video makes a pretty convincing case.