A seeder is a peer which is serving a complete a set of all files. Peers which are not seeds also uploads, and this is not called seeding.

Yes, I didn't think that extra nuance would help in this situation. The person I replied to wasn't familiar with bittorrent terminology so adding in the complexity of whether or not you have the complete set of files is unnecessary for this discussion. But yes, you are correct and my statement was technically wrong/incomplete.