Apple Watch setup without an iPhone?

The Apple Watch needs the iPhone to be powered on and able to access the internet, plus you need to be signed into iMessages on the iPhone. The Apple Watch will relay all SMS/MMS TEXTing to the iPhone.

The Apple Watch cellular radio is a data only radio and can only access the Internet side of the cellular company's business and does phone calls over VoIP. Not having a traditional cellular radio, it cannot access the cellular SMS/MMS TEXT messaging packets.

Use your Apple Watch without your iPhone nearby - Apple Support

Read the the first footnote:

1. To receive SMS, MMS, or push notifications from third-party apps on your cellular Apple Watch, your paired iPhone must be powered on and connected to Wi-Fi or cellular, but it doesn't need to be nearby. You also need to be signed in to iMessage on your iPhone.

Rude is an opinion. I thought I was trying to provide facts, and save someone from buying an Apple Watch and being happy with their purchase if they did not own an iPhone. 😞

The family plan is most likely what the family you mention was using. Still need an iPhone, and the Apple Watch does have limitations, because it does not have its own iPhone paired to it:

Set up Apple Watch for a family member - Apple Support

Apple extends the Apple Watch experience to the entire family - Apple

Yes. Everything I said is for a Cellular Apple Watch 📶

😁

• Apple Watch needs an iPhone to setup
• Apple Watch needs an iPhone to update software
• Apple Watch needs an iPhone to send and receive SMS/MMS TEXT messages
• There are other things the Apple Watch depends on the iPhone for.

If you are not an iPhone owner, or the child or aging parent of an iPhone user, you should consider a different smart watch manufacture.

Unfortunately you need to pair the apple watch for the first time with an iPhone. As far as I know you cannot set it up with another non-iphone phone.