The program "cd" can only navigate into directories mounted to your local VFS, and a URI that starts with "smb://" describes a remote resource. In order to cd into an SMB share, you have to mount it.
In your case, it sounds like the SMB share was already mounted and accessible from nautilus. That means the SMB share is already mounted somewhere in your local VFS.
In Ubuntu 15.04, I believe the default mount point for SMB shares (at least the ones you connect to using nautilus) is:
So instead, try:
$ cd /run/user/$UID/gvfs/smb:host=server/path/to/file.txt
Edit: For a more in-depth explanation of this, here is a similar question on unix stackexchange with some great answers