IT could be an iOS issue. It could be a Siri on the watch only issue. It could be an underlying BSD issue. It could be........
I never would have known about this issue had I not read about it. For those who do application testing, they know no matter how well you test given the best plans and best intentions, you only catch 30% of the bugs. That's it. Beta testing may help improve that a bit, but it's still a small number.
For those complaining about how the issue caused the watch to completely reboot, it didn't. A post earlier advised what kind of action was taking place. Go find it and read to understand.
For those concerned about the security aspects of this "bug", your imagination is going quite wild. Unless you establish your OS security acumen and how you have personally reviewed the source code to reveal a potential security threat, stop with the BS. iOS is still the best and most secure OS for small devices out there.