Well--those are indeed coming from your computer . .. but they have to be listed in black in your Library in order to be eligible to be uploaded to others.

Check your Library to make sure you are only sharing the folders and files you want to share.

Also, as you download a file, those partial pieces are also eligible for others, much like the way bittorrent works. It's called Partial File Sharing in Gnutella (PFS), and really helps speed sharing of files. Perhaps those pieces are what might be surprising, since with PFS file names that you haven't completely downloaded are already being shared.

If sharing PFS files are bothering you, clean out the incomplete folder.

Cheers (from one old guy to another)