I love the idea of having lens distortion correction based upon the lens used, but it seemed odd that for a Nikon camera, sigma was the default lens? Also, I thought the meta data would be used to determine the lens. Great feature, though.
Unfortunately some of the metadata used to identify a lens is ambiguous. But you can override this automatic matching (in case ACR/LR doesn't get the initial guess correct) by choosing "Set New Lens Profile Defaults" from the Setup popup menu (in the Lens Corrections panel).