Please read it again. It doesn't say that non-commercial use is allowed, it says that this may be a factor in whether the use is "fair use" or not.The purpose of torrents is not for commerical use, so not barred.
And your computer stitches all these together to create a complete version of whatever it is you're downloading. You still end up with a complete version. The fact that it was assembled from many pieces doesn't change this fact.And you aren't actually downloading 30 second clips. You are downloading 2000 seperated 1/4 second clips from all over the complete video. You fill in the blanks from other users.
Personally, I'd say that acquiring a free copy of something to avoid paying for it is a commercial use.Certainly, people sharing books is an 'educational' use, not a commercial one.
Maybe it would help if you read the examples of fair use that they give:
The 1961 Report of the Register of Copyrights on the General Revision of the U.S. Copyright Law cites examples of activities that courts have regarded as fair use: “quotation of excerpts in a review or criticism for purposes of illustration or comment; quotation of short passages in a scholarly or technical work, for illustration or clarification of the author’s observations; use in a parody of some of the content of the work parodied; summary of an address or article, with brief quotations, in a news report; reproduction by a library of a portion of a work to replace part of a damaged copy; reproduction by a teacher or student of a small part of a work to illustrate a lesson; reproduction of a work in legislative or judicial proceedings or reports; incidental and fortuitous reproduction, in a newsreel or broadcast, of a work located in the scene of an event being reported.”
Note that there is nothing in this list that's anything like "getting a free copy from someone else because you don't feel like buying it."