Can LR CC original raw files in the cloud be downloaded to computer?

The simplest way to do this is to go into Lightroom CC's preferences. Go to the local storage tab. In storage location for originals select a folder on your external hard drive. Then select "Store a copy of all originals at the specified location" and hit done. Lightroom CC will download all your originals to the external and your backup will back those up to your online backup. Any new file added to lightroom CC will be copied to this location.

You can export them using Save To (Original + Settings).

If you want the whole library downloaded, then you could ‘select all’ in All Photos and follow the above.

However, it would probably be better to use the downloader tool: Download synced Lightroom photos and videos from the cloud to a computer

Note however, the actual downloaded photos will no longer be linked to Lightroom. So any further edits to the Cloud files will not affect those that you downloaded to your external.