Yes, we can easily surmise this is a software issue. What we don't know is which software at fault, or even more critically, why some watch owners are affected severely, some moderately, and others, not at all. The difference can't really be explained by how the watches are used. We have two in our household and both are used in essentially the same way. One is unaffected. The other drains far more quickly than before (but not as badly as some report here).
Personally, I suspect it's got something to do with wi-fi or Bluetooth, a theory that wouldn't be difficult to test. A person with severe battery drain could turn off wi-fi on their watch and keep their phone in pairing distance for a few hours and see what happens. Then try the same with Bluetooth.