actually soloing is not "free climbing with no equipment." in reality soloing is climbing, be it free, aid, ice or even alpine climbing with
gear but sans a partner
. hence the word "solo
now what siren is referring to is actually what's termed "free soloing" where it's done alone and without gear. there's a good book written by John Long, called The High Lonesome which delves deeply into the world of free soloing.