Published by Timun Mas (the publisher of all TSR novels in Spain), not by Zinco (the publisher which produced the 2nd Edition AD&D books, including DragonLance).  It was transformed into an Appendices book for the DragonLance Chronicles, and released in novel format (first a hardback with dustjacket, later a paperback).  "Clearly, it was never intended as a gaming (or gaming/novel crossover) product. My guess is that Timun Mas capitalized on the 'Tolkien Trilogy' style and saw that releasing an Appendix book (like the Lord of the Rings Appendices) was marketable." Thanks to Andrés Otero for this info, and the scan.