Well it looks like the one who told you i-dont-bang-random-people thing mistakenly put themselves in that terminology. Demisexual is much more than that, it's just not about bang who and when. They don't feel any sexual and physical attraction like at all and don't think anyone is HOT for that matter. They will only develop sexual attraction or physical appreciation for someone they have strong emotional connection with which processes gradually over time. Demisexual falls between sexual and asexual category and it runs deeper than just I don't want to fuck random people thing. When someone who says it, they can be a demisexual but in most case they are not. If this description confuses you, then I'll say that demisexuality is basically asexuality but later possible to develop sexual attraction due to strong emotional bond. You can check the whole definition and explanation on the net as I assume you don't read anything about demisexuality.
Goodluck.
P.S I have to disagree with your "most of the world's population obviously would fit under the 'demisexual'.. " statement because by even your logic, even that someone doesn't want to bang anyone random, they will still feel that attraction (which contradicts the whole point/definition of demisexuality, if you read any). And if you look closely to our world now (based on status quo) the point is invalid, since not few people today simply want to bang anyone they found attractive whether they familiar with the person or not.
