I also see the word used this alternate way, and as a teenager, I came to the somewhat flawed conclusion that all acts were selfish. Even a martyr behaves selfishly because they get satisfaction from their martyrdom, or so I figured. I do think this perspective was adopted by many children of the 80s.
It wasn't that long ago, that I shared my perspective on "selfishness" with someone else, and it was pointed out to me that I had rendered the word completely null. If all things are "selfish," the word has ceased to have any useful meaning. If "selfishness" encompasses all things, it doesn't mean anything at all.

That doesn't really stop people from using it in all sorts of inappropriate situations, however. I agree with the poster above about this new usage being related to libertarianism and objectivism. I believe there is actually an intentional blurring there. If rescuing a kitten, and telling a homeless man to go fuck himself are both "selfish" then I no longer have the language I need to differentiate between a social act and an anti-social act, and am relieved from my sense of responsibility and guilt.

No, you are 100% right. There is a correct way to use the word "selfish" and an incorrect way. And more than that, redefining it in this way is damaging to society imo.