Look at this exploded view of the fuel tank.
172 Fuel Tank :: Fuel & Engine Control :: Genuine Nissan Parts :: 370Z Parts (Z34) 2009+ :: Nissan Parts, NISMO and Nissan Accessories - Courtesyparts.com
The sender has a float on the end of a metal arm. This arm can get bent, and a hard impact from a collision could certainly be enough to do that.