Your school might've ranked people based on a decimal system however for the marks given to NESA as your internal mark, they are rounded to integers. Although some people lost more marks, cumulatively your final internal mark and their final internal mark may be, for example, 89.8 vs 89.6. Based on your school's ranking (decimal system) you are ranked higher, however NESA would see that both of you students have been given a 90 internal assessment mark and thus tied. I am tied with atleast 5-6 people in my advanced cohort aswell on my NESA ranks, but prior I was ranked 2 positions higher due to my school's decimal system.