That was an old bonus that we removed because people kept forgetting about it. Nothing in the way the cavalry looked suggested that you would get such a bonus. Compare to the new Armory, which is obviously something different.
Manuals are often begun long before the game is finished so that they can be translated to many languages, and we love to tweak things up until the very end. So, it wouldn't surprise me at all if there were some errors in the manuals, though we tried hard to avoid it.