Rules Analysis
If the thrower accidentally drops a live disc or a disc in play without defensive interference and it contacts the ground before the thrower regains possession, it is considered a turnover. If the thrower regains possession of an accidentally dropped disc before it contacts the ground without another player touching the disc, that possession is considered continuous.
An accidentally dropped (falling, non-spinning) disc is not considered in flight. An accidentally released, spinning flying disc is a throw, not a dropped disc, and results in a turnover if the thrower regains possession of the disc without another player touching the disc. And the stall count continues uninterrupted.
A pass is intercepted if a defensive player obtains possession of the disc, but if the defender accidentally loses possession of the disc before or during ground contact related to the catch, the pass is considered incomplete rather than intercepted.
i.e., this is not a "double-turnover" - the defender's team still gains possession.