The twisted loop is a "bimini twist" knot, hence the name of the tippet. This is a standard knot for "big game" fishermen who are trying to catch fish on tippets with a certain class of breaking strength. The bimini twist knot is a 100% knot, so no strength is lost in the knot.

Here is a link to how they are tied:
http://www.leadertec.com/tipsandtech...ts_Bimini.html

Ted