E-publishing can be a self-published book just like a paper book can be self-published.
Exactly.
While it's clear that you understand the difference, the reasons we tend to explain is because so many people come here, or lurk here, and DON'T know the difference. They assume that all ebooks are self published.
Epublishing has made self publishing much easier for the author. The costs are lower for a start, and it's much easier for the author to complete the process.
That said, there are some very good printing service, such as Create Space and Lulu where an author can self publish a print book for virtually no cost.
So, as you can see, the options for the self publisher are vast, and they are increasing all the time.
This is good for the self publisher from the point of view of accessibility, but also when considering how and when teh author is going to get thier product to a reader. In self publishing the author has much more control of timing - such as when to release their book, before christmas for example, or push it back to summer, where they wouldn't necessarily have that option with a traditional publisher.
Obviously self publishing has it's downsides as well. Primarily the loss of the support is huge - it's amazing what a publisher actually does, everything from covers, to formating, to organising printing and distribution, promotion, placement and the finance to support the book in these things. Most self publishers don't have the finance or the pool of resources behind them to achieve the same things as publisher.
This is part of the reason why a self published book is often of lower physical quality, if not the contents.
This isn't a slur on self published authors (hell, I am one). But when the writer is ultimately responsible for the book and it's contents, it can be hard to see things objectively. It can be hard to spot the typos when you have read the same page 20 times.
Having been on both sides of the fence, I can tell you first hand that self publishing is not really for me. I've tried it and it's exhausting. I just don't have the drive or the ability to really make it work for me. It takes so much more time and effort to get anywhere. Which is why I respect someone who manages to self publish successfully, because although it's easy to self publish these days, to self publish well is damn hard.