If your download says 100%, it's downloaded = complete.
We know the terminology is a bit confusing, but it comes from the BitTorrent network and how it works.
BitTorrent is a P2P network that FrostWire connects to, among other places. If you download a file from that network, you can also seed it (upload it for other users to download) after your download is finished.
If your seeding setting is set to 'Do Not Seed Finished Torrents', FrostWire will download the file and then stop all transfers [some seeding will still take place during the file's download per design of the BitTorrent network). That's all it means.
Notice that if you tap on the menu next to the file, you have an option to Seed. If you tap on a menu next to a file you downloaded from a cloud source (from a network of servers) you will not get that option.
See more on BitTorrent here, if you are interested.