No thats not conjecture. It was reported so. Apparently Jerry Jones was miffed that Richie Waited till last minute or something like that to inform that he wasn't coming back etc. Anyway, I don't remember the reason, but Jerry didn't like the way Richie handled some of his responsibilities.
It was reported by DMN and probably Star Telegram. And I yeah, it was also reported he wanted to try to coach with Cowboys and the reason he didn't do it was because of Jerry not liking. It wasn't a major news item, so you probably might have missed it, but it was repeated and not really a rumore per se. Jerry outright didn't say that in an interview etc. though, if thats what you mean by conjecture.