They must have changed the rules.
Before I got my A-10 assignment (I was a FAIP), I was under that same impression. However, went to RTU and received LOAC training and found out it was not a violation of LOAC to use the gun on troops. Thing is, if you think about it, a tank, truck, bunker, they all have people in them and you are trying to kill the people (if not the vehicle). And, at what caliber is a gun “too lethal” to be used against troops?
It is the 30mm part I think that gave birth to the idea you can’t use the gun against people. . .but the Apache has a 30mm (not the same power, mind you), and no one questions the use of that weapon.
Cheers.