I'm more intrigued by the presence of the dragon actually. I'm guessing there's expansive tunnels we didn't get to see/possibly collapsed that he used to enter the area ages ago.
I actually feel bad fighting him. I kind of get the feeling he came out in the first place because he heard me shout and thought he wasn't alone anymore.
He got killed by the Falmer and their servants before I could even get near him.

I wanted to let him fly freely through Blackreach, but alas, he thought it was more interesting to fight the little guys.
About the giant, I guess he stumbled on the elevator like Lord Vukodlak said. Nothing I can help him with 'though, I don't speak Giantese.