Could be both.
According to SERoundtable, there were lots of reports of a Google update between the 1st and 5th: http://www.seroundtable.com/google-nov13-update-17630.html
Anyway, is a not-confirmed update so it could also be the disavow file doing its work. If some of the links you disavowed were the reason of the ranking drop, then you actually got those rankings with artificially created links. So don't remove them from the disavow file because of the drop, just focus on getting new ones. How? Content!
Hope that helps!
I was intrigued...