something they didn't mention, what is in this upper stage? I'm presuming a rocket motor and some fuel is that right..? They do a calculation of energy release on impact, but I'm wondering if there is any fuel left and whether that would affect their equation?

I can't really think of much besides maybe some batteries. The fuel and oxidizer are supposed to be dumped shortly after payload deployment to prevent any issues with blowing up. Even if it wasn't dumped, its been a year, so it would have boiled off.