That's a great point. to me it looks like he either didn't fit...

That's a great point. to me it looks like he either didn't fit the company culture (or friction between staff) or he was struggling to "get his feet under the desk" or get his head around the job if you will. 6 months is around the time you should be getting comfortable in any new job and it appears he doesn't have anything else lined up otherwise it would say where he is moving to. No-one would walk away at such an exciting time as this without a decent new prospect.

Its unusual they didn't find a replacement but looks like his position has been absolved into the other roles anyway. Either way It seems like it was a sudden departure.