I up-voted you because yes, you are correct and I fear people who read the article won't get it.

But the article was written to highlight this - when you state honest opinions you ARE being a selfish prick.

There is a point in the article when it is suggested to write "I resent it when" or "I appreciate it when" - the choice between the two is where ego can interfere. If all you communicate is resentments (as the article plays up for entertainment), people will come to view you as a negative dingus not worth talking to.

But communicating honest, positive statements is what people should aim for - only going for negative when it absolutely needs to be said.