In the movie,while the Corleones are waiting to send Michael to the Sol hit,there is a mention of the "negotiator" playing pinochle with Clems men,amd that until Mike comes back safe and sound,he keeps playing cards.
I wonder if Coppola used that phrasing instead of 'hostage' to avoid going into an explanation of the Bo's. I think by this time in the production, only stuff really critical to the story was going to be included.
The book does use "negotiator" as well as "hostage." It would sound pretty odd to say the hostage is happy, they're letting him win.
When he was annotating the novel, Coppola just crossed out pages related to the Boccicchio. It could be that he didn't even process that the Sollozzo hostage was a Bocchicchio.
