Hi,
Spagiola's explanation of expressing a sentiment of extreme frustration close to anger, was much better than yours.
When you don't understand something ... you can be frustrated a max .. certainly if you (or think) know many things ...
So .. c'est pas possible can be an exclamation caused by something beyond his understanding
Anyways all is open .. and again .. this must be not important in the cause of the accident
The most important words are "j'ai les commandes" and the actions immediately following.
If those actions can be explained by other thing than a "pilot error" ... maybe this accident will bring some (new) progress for the aviation safety