There is so much unattributed or wrongly attributed stuff circulating around the Net the video creator likely didn't know where the music came from. I see virtually every spoof song being accredited to Weird All Yankovic and every rant being claimed as coming from George Carlin. Mostly, folks don't care.

But I agree, if you use something like that, you should make the effort to give credit where it is due. (and notify the creator if possible, chances are good they will be amenable to its use.)