I haven't seen this Q&A, only the Reddit one where he says the sword is more like a "robot spren". I'm not sure "broken" is the correct word, more incomplete. NB is sentient but kinda dense despite its age, whereas a spren the longer it's bonded has picked up on mannerisms and learned much to be much better company. Not gonna lie when I finished WoR I was psyched when Szeth got this sword, but after reading Warbreaker I was kinda let down after finding out how NB isn't very smart.
Anyways back to the topic, who do you think Gavilar was trying to keep the stone from? He assumed Szeth was Thiadakar's assassin. When he found out he worked for the parshendi he gave him the stone. Was he trying to keep it from the parshendi and was frazzled due to the fall/beating/having a chunk of wood through his chest? Or was he attempting to keep it from the Ghostbloods?