If you read the text before the link concerned here you can get a good idea of what it was, an excerpt from a movie. If it was a link to a trailer of a movie on a site like IMDB I'd say that is different since they probably got permission from the movie people to post that trailer, it was not taken.

Youtube is a nice fun invention but they routinely break copyright laws, they are currently being sued by at least one group right now. We cannot assume that just because it is from Youtube that is is 100% legal.

It's late and I'm tired, I hope this helps.
More questions ask away.

Gs