Thanks
All it means is, the top academic achiever (overall 1st rank) is nominated by the school for the scholarship. I'm not sure how your school determines the top academic achiever, although if that guy your competing with ends up beating you (lets say), and you come 2nd, if he has at least 1 UNSW preference in his UAC preferences, then he will have to be nominated for the scholarship. However, if he has no UNSW preferences, then you would be the next up for nomination.
At my school, the guy that's coming 2nd, or close to 2nd, has most of his preferences at UNSW, and would've loved the UNSW scholarship.. although he didn't top our year (plus he's an arrogant asshole LOL) and the principal (who favours this student) couldn't actually nominate that guy for the scholarship.