So you just scan for devices and then read? There's no authorization involved, these just publish the readings wirelessly for all interested?
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It's problematic for things like keyboards used for entering passwords - but if my next door neighbour wants to snoop on my living room thermometer or someone wants to snoop on my heart rate strap as I jog past their house? It doesn't seem to be much of a problem, in practice.
In the bad old days of bluetooth, loads of devices without screens would just hard code the pairing code to 000000 anyway. So it wasn't adding much security anyway. Unlike internet-connected devices, it's not exposed to a billion griefers from around the globe at any given moment.
The most similar device I've worked on is the various Oculus devices. Which will also accept bluetooth connections from absolutely everyone, but the first time you connect you store an encryption key that is used to secure all subsequent comms.
Oculus decides are pretty big, I assume they have buttons that allow you to recover from that. This ring doesn't.
Even most input-less smart devices have a way to do that though - like those ridiculous smartlight bulbs where you have to flick the light switch on and off in morse code to trigger the factory reset