That is because there are actually two different packages in the same zip file. I'll put some installation instructions in the next readme file. You should put EITHER, the plgx file or the contents of the DLL directory into your KeePass install directory. I have included both in the package because some people like the DLLs over the plgx file but the plgx file is really the simplest way to go. Since you extracted the entire zip file, you have in effect installed the plugin twice. KeePass will dutifully load each separate package individually. Delete either the KeeCloud.plgx or the dlls (awssdk.dll, DropNet.dll, KeeCloud.dll, RestSharp.dll)
I apologize that I wasn't really very clear about how to install the plugin.