I have a 66 Monk/Druid combo and have few problem with PoStorms. One thing I learned was keep your eyes open and don't "pull" mobs. Animals all have social argo. Go to the mobs and fight them where they are. You do have a chance to get an add if mobs walk by. But, if you go and pull and mob, then bring it back, you could argo several wandering mobs while returning to "camp".
On the first "island" the mobs are fairly spread out with a few wanderers so it's fairly easy to fight one in place without getting adds. If you go past the river to the second "island", Then you increase your changes due to all the wandering mobs. On the second island I have had 3-4 mobs end up on me when I started fighting one mob.
On the 8 or 9 mob pull, my guess is two things probably happened. There was a train elsewhere that he picked up, or he ran close enough to several wandering mobs to get argo. But I am guessing it was a train he hitched a ride on.