As I recall, the end of the release cable has a ribbed fitting (I don't know what else to call it) on the door end with I think 4 or 5 ribs that create grooves in the fitting. These grooves fit into a slotted holder beside the gas cap door opening (inside the fender). The slot in the holder is a V with a hole in the bottom of the V and the cable end fitting gets pushed down into the hole and is held in place by the V. The purpose of the grooves is to allow you to position the release back and forth as required. If you banged the cable hard enough you may have popped it out of the slotted holder and it is now flopping around. In the worst case you may have broken the fitting on the end of the cable and require a new cable. There is a rubber 'thingy' in there; but, I don't think it has anything to do with the release cable.
Its been a few years since I was poking around in there and I was looking at something else, so my recollection may not be spot on. With the fuel door open, have a look at the rear side of the fuel door opening where the release should be - maybe you can see the holder for the cable and it should be obvious if the cable has just popped out. My car is in storage so I can't get access to have a look at the fuel door release. I don't know whether you could re insert the cable from the fuel door opening. I have this bad feeling that you may need to remove the fender liner. Fender liner removal would be a definite yes if you broke the fitting on the end of the cable and need to replace the cable.
