User blog comment:Martialmaniac/Nen beats page/@comment-31525652-20170825004101/@comment-5780397-20170825101136

From what I gathered, Nen beast and parasitic type are two different things altogether. As I've said, Nen beast is a term that has been used in the past too to describe semi-autonomous Nen constructs, while parasitic type refers to how they are made: the Guardian Spirit Beasts are at the intersection of those two ability types, as they have been consistently described both ways.

About Conjuration, Bill was speaking about parasitic Nen in general, as you aslo pointed out, but the beasts we saw being conjured would contradict what has been said up until this point about conjured objects being visible to everyone (and they cannot be hidden with In, since the Hunters do not need Gyo to see them). Maybe most parasitic type abilities are curses like Judgment Chain and Countdown, which would explain why many of them are Conjuration based. In fact, Bill's explanation seems to refer to abilities that are harmful to the host instead of helpful, as is the case with Guardian Spirit Beasts.