Is the plug-in only 32-bit? You might test in the 32-bit version and see if it works?
I've checked that the basic file Fitsplug.8bi works with PS CC 32-bit. The editor cannot ensure that the last V2 version Fitsplug2.8bi is suitable for PS CC 64-bit as this is untested. He intend to look but will be surprised that the CC architecture is different of the previous and suitable CS 64-bit.
The architecture of Photoshop has not changed.
It sounds like the plugin author might be a little confused, however.
How hard would it be to just try it?