Re: Note that they didn't bother with open source operating systems
You're very charitable, I suspect they just didn't think.
OpenBSD has been included in embargoed fixes before, and slipped the changes into the codebase so users were protected on day one of the public notice.
Knowledge probably wouldn't have leaked from the BSDs unless someone was watching commits for all four of the main BSDs (fourth : DragonflyBSD), but yes, if every single OS out there is informed sooner or later it will leak.