How exactly do you tell the difference between a bad game and intentionally feeding?
It's extremely difficult to discern intentionally bad plays much of the time. The automated system isn't always very good at detecting it, but it's tuned conservatively enough to almost never flag a bad game as intentional feeding. Even a manual review will have a tough or impossible time determining malicious gameplay.
As for false reporting, is it perspective thing?
It's determined by the community standards. The system actually uses machine learning to improve its detection and learn what players take issue with, so that it only punishes behavior that the community is largely against. If you alone take offense to people saying "GGWP" when you had a bad time, your reports for that won't ever get anyone punished because basically nobody else actually thinks that way so you're the only one reporting like that.
There are a lot of intricacies of the system which are left intentionally vague so as to prevent gaming it, so some questions may only get general answers. You may learn a little bit more about the IFS here, though; https://support.riotgames.com/hc/en-us/articles/207489286-Instant-Feedback-System-FAQ-