This is some weird sense of humor.
My guess is that it also serves another purpose since the uncompressed file came out as “How.I.Met.Your.Mother.S06E18.720p.HDTV.X264-DIMENSION.mkv”.
Maybe that’s a trick to upload the file on rapidshare and the like without having the file removed.
I took that screenshot here.
Since it’s a bit torrent site, it makes a little less sense to have the files named that way. The guys who uploaded the torrent probably didn’t even bother renaming it.