It should be required that anyone writing an Amazon review should read the introduction to the book. I'm amazed how many people skip right past an authors intro and go right to Chapter 1.
The priest who blames Borg for citing himself would have not written his review if he had actually read Borg's introduction to the book. Prior to writing The Heart of Christianity, Borg published Meeting Jesus Again for the First Time, and Reading the Bible Again for the First Time. Borg says in his introduction that The Heart of Christianity includes a lot of what appeared in those previous two books as well as others, but this book puts it all together. So, Borg cites his previous work. Not exactly a crime especially considering Heart of Christianity is the distillation of most of his previous works.
After reading this, seek out the other two books I mentioned for more depth into Borg's message.