Last night I updated to the latest software on a series 2 watch and this morning the screen broke away for no obvious reason. Is that likely to be a coincidence or is it possible the upgrade could cause a pressure increase. I read about a battery issue on older watches can sometimes pop the screen out but this was a catastrophic blow-out and the watch now has no display or signs of life!
The only thing an update might indirectly cause is heat, and when the update completes sound a tone, and maybe vibrate.
That kind of failure is typical for the battery swelling problem. In other words, your Apple Watch had a pre-existing condition, and it was only a matter of time when it became visible. The software update might have created a little extra heat by sustained processor activity, but that screen was already a problem looking for an opportunity to happen.