If you give your five year old a handgun and he shoots his little sister dead, who’s to blame?
I think it plausible that Pro-Russian rebels would have been able to fire the weapons – they are battlefield tactical weapons designed to provide Anti Air coverage for tanks and APCs in the field.
While they probably don’t come with a big red button marked “FIRE” I doubt the Soviets deliberately made them complicated to use. After all when when you are providing AA cover for a bunch of tanks you don’t really want your conscript operator to have to go through a 10 minute checklist when an Apache gunship pops up and starts targeting the tank column you are protecting with a Hellfire
If Russia has supplied these weapons then they are ultimately to blame, whether they had a hand in actually operating them or not.