Fernando: Two new Watchtower classifications were suddenly created: "true religion" and "false religion".
WTS did not create those categories; they were always part of religion. Every religion considers itself the true religion, which means the others must be false. The WTS emphasized it because Rutherford seemed to revel in being a contrarian (and an asshole).
As for how to define religion... Google the word and you'll get a whole bunch of different answers. No one seems to know for sure how to define it. I think it's just another form of tribalism, a way in which humans form us/them groups to foster a sense of belonging and to build strong social bonds (the irony being that those bonds come at the expense of enmity with 'them').
These groups form organically because they are so intrinsic to how our minds work. And we join them almost by force of habit. We 'belong' to groups based on ethnicity, nationality, geographic location, color of our skin, color of our hair, dominant hand, favorite sports teams, and so on. Religion and government are the ultimate forms of this behavior, as they can justify the most extreme acts taken in their 'defense'. Human history is an ongoing effort to mitigate the dangers of both, a battle we seem to be winning, albeit very slowly.