Because when the suspension travels the wheels dont just go up and down, they tuck into the arches slightly at the top too. So by dropping the car by 30mm, you will have the top of the wheel tucked slightly up and inside the arch, i.e. negative camber. Also because of the suspension system on the zed, with negative camber comes toe in as well. So, changes are after dropping the car by 30mm, you'll have camber of around 3 degrees, (2 degrees max in OEM specs) and several mm of toe in (2.7mm max in OEM specs).
The zeds OEM adjustments arent enough to bring it back in to line a lot of the time. So it's best to get it checked and adjusted. If it cant be adjusted enough, you'll have to buy a rear caber kit.