My friend dreamed that I had published a book.

1, you are friends who communicate frequently. He knows that you have a good writing style and a strong literary atmosphere. Moreover, the dream he had last night was a beautiful dream, so all good things can happen, and your book publishing situation is more in line with your own image. (So it's a coincidence, a reasonable coincidence)

My friend didn't have this dream, just joking with you. (How likely is it, judge objectively by yourself)

In fact, this is not dream interpretation now, but reasoning. This dream can best explain, only your literary temperament image in the hearts of friends. The reason to explain this matter lies in your subtle psychology of hoping that good things can happen.

I hope it helps.