Reddit reviews The Beauty of Kinbaku: (Or everything you ever wanted to know about Japanese erotic bondage when you suddenly realized you didn't speak Japanese.) Second Edition - Completely Revised and Updated

To really know the difference between the two, you have to look at the Japanese. Shibari (縛り), the nominal form of the verb shibaru (縛る), which means to tie.

Kinbaku (緊縛) is used to refer to sexual bondage.

Shibari is generally more artistic and doesn't need to involve nudity and/or play.

You can get a much better description of both from this book:
https://www.amazon.com/dp/0692344659

Both shibari and kinbaku come from hojojutsu: https://en.wikipedia.org/wiki/Hoj%C5%8Djutsu

Hope this helps.

The Beauty of Kinbaku discusses the history from hojojutsu to kinbaku very well. Essentially, the idea is that hojo was used in historic battles to capture important people.

Later, they wanted to portray this battles and capture scenes in plays. But hojo ties were both dangerous and difficult to see since they were almost entirely on the captured person's back. So this led to the development of less dangerous ties that had "front" elements that could be seen by the audience without the tied person having to turn their back to the audience.

It's a fascinating book!