This is not true unless it’s changed as I contacted both Apple and AT&T multiple times to clarify this when series 3 cellular came out 2 years ago.
That's not what these say:

How to Call 911 from Your Apple Watch in Case of an Emergency
When you can't reach your iPhone or don't have it on you, how do you get help from emergency services? Unless you have one of those life-alert mobile...


Apple Watch LTE can make 911 and emergency calls without a carrier plan
A Reddit user recently discovered that an LTE enabled Apple Watch can make emergency calls even without a connected phone or even a carrier plan. …

As I see the Watch becoming more of a central device, I’m predicting Apple makes the design wider to add more horizontal screen real estate. I rendered a mock-up.
That's an interesting mock-up!