User blog comment:Rrr2015/FEITAN...a Zoldyck?/@comment-5780397-20151110114649/@comment-5780397-20151111124351

Yup, but Kalluto never mentioned Killua's name, and by saying that it's Killua, we are leaving out other possibilities, so this too is speculation in a sense. The fact that I'm entirely convinced Kalluto is talking about Killua is another matter.