not that much... its a rough estimate of your cohort's performance... so if you have a better cohort than last year (school rank) then obviously your atar will get pulled up
lol I think he/she is just venting and hoping to find comfort by telling him/her that he/she is okay for the externals.
so...... yeah you'll be fine! 86+ is a possibility especially with marks like that in ext1 and 2 maths