Tim Bajarin, writing for Time:

The late Apple CEO Steve Jobs developed pancreatic cancer in 2004. He then spent a great deal of time with doctors and the healthcare system until his death in 2011. While that personal health journey had a great impact on Jobs personally, it turns out that it affected Apple’s top management, too. During this time, Jobs discovered how disjointed the healthcare system can be. He took on the task of trying to bring some digital order to various aspects of the healthcare system, especially the connection between patients, their data, and their healthcare providers.

And:

It seems clear that Apple’s management has now and will continue to have a major focus on bridging the gap between a person and their healthcare providers. I believe Apple is on a mission to improve the overall health of its customers as well as that of the healthcare system, a task Jobs gave them before he died. And while Apple’s products define Jobs’ legacy, it may turn out that his and Apple’s greatest contribution may be to bring greater order to the fragmented healthcare world.

It is within this backdrop that the Apple Watch was born.

The sense I get from reading this is, though Steve may not even have been aware of the Apple Watch design effort, his battle against cancer was a major motivating force behind the Apple Watch design and creation.