All this vitriol seems like an over-strong reaction to an executive panel rescinding his offer. Canonical should definitely have been clear about the entire process up-front, but making decisions before you have a full confirmation doesn't seem sensible.
When we hire we send out an offer letter after all the interviews are done, but that offer is explicitly still contingent on right-to-work checks and satisfactory references. This is normally a formality but there's always a chance something might go wrong.