I wonder how such hack would even work. The watch does have the option to control it remotely, through the iPhone accessibility options, but obviously this only works with the paired iPhone and not over the internet.
That's the intended design, but perhaps the trusted device layer could be bypassed under some circumstance? It seems extremely unlikely, but maybe not impossible.
edit: The more I read and think about this, the less I think it's likely. I'll keep this as a devil's advocate sort of message, but I feel like I should still point out that the entire premise here seems a little nuts and the people reporting the hacks are more likely to be uninformed/paranoid/etc and dealing with ghost touches than the watches were likely to be compromised.
If this is for real I expect we'll hear more about it soon enough.
Nevertheless, this does seem like an anti-Apple campaign.
It would almost certainly would be illegal.