If you are logged into your Autodesk account in one piece of software and accessing cloud services you are also logged in for any other Autodesk software you have open at the same time. In other words you have one login for all software. So for example I am working in Autodesk Infrastructure Modeller (AIM) and am sharing scenarios to the cloud. At the same time I have Civil 3D open and am working away on a project. I want to stop Civil 3D syncing to the cloud but cannot log out of my Autodesk online account because I am uploading from AIM.
The solution is to prevent C3D from automatically syncing. In C3D type OP at the command line and in the options dialog box, online tab you can untick the boxes in the following screen grab. This will prevent C3D automatically uploading to the cloud.