I'm saying that whoever was proving a violation would have to show infringing distribution of a protected work. Bit torrent pieces generally contain a small fraction of the total work, which could easily be fair use. You'd have to show that the person was actually transmitting a protected work against its license. That piece may have been a short clip in a more encompassing work. You won't know until you get more of the context (other pieces).

So, maybe "they" (person/group alleging infringement) wouldn't have to get all the pieces, but it makes their case much stronger. There can certainly be fair use arguments made for transmitting torrent piece sized copies of protected works.