Really ??? no one care about Kerrigan Q Quest ? Still Bug and Finish Quest in 5 min , gain 5 stack with killing minions
what the hell is this ?
EDIT2: I stand corrected… after further testing it seems actually like its bugged (sometimes).
if ravage actually kills the minion it counts as 1. If it dies after ravage within the 1.5 seconds it counts as 5 regardless of lvl 1 pick… 
If you pick Fury of the Storm on tier 1 your next basic attack after using ravage does splash damage. Said splash damage counts as damage through ravage.
That means:
you use ravage on a minion = 1 Stack
next basic attack hits 7 minions = 7 stacks on top of that.
since you got 2 charges of ravage double that = 16
now they simply have to die within 1.5 seconds after your initial ravage usage, which is easy if you initiated with primal grasp.
try finishing the quest without fury of the storm, if it still goes out of hand i am wrong but this is my best explanation here.
I do care about kerrigan 
edit: to clarify my point here: you can apply damage through ravage directly or indirectly multiple times per minion.
i hope i could help. cheers