Happened to my series 0 after I moved to the Philippines; a very hot and humid environment. The battery swelled and popped the screen off. It was one of the very first manufactured, received on that day back when everyone was going unboxing videos. Was that April 24, 2015? Seem to recall that as the date. I drive a series 2 Nike Edition now. Love it. Nothing lasts forever.
I know a fair number of people with the Apple Watch, and none of us have had this problem. We know it happens, but there are tens of millions of these watches out there. If it was a really serious problem we would have heard more about it.
The $5 million is a trap, if Apple decides to just pay it off, the law firm will hit with another much larger suit and use this one for grounds