Companies ought to be more upfront about their salary bands. It's pretty unreasonable to have candidates jump through a phone screen, complete a homework assignment, then travel to come meet in person for the whiteboard pain session before they know if a company can even afford them. I see more companies getting this right lately but we have a way to go.
Otherwise, it can be a huge waste of everyone's time. In this case it sounds like whoever negotiated didn't even have authority to make a deal, which is a pretty big flub on Canonical's part.
The other possibility is that one of the interviewers didn't get feedback in before the negotiation. That would still be a process fail.
A good developer/SRE should basically be able to justify her expense and essentially write her own check, splitting the value capture with the host company. Things are way off and asymmetric in the current hiring practice.
Thanks for posting. It's understandable to be upset here. More companies with bad interview processes should be outed so that they can improve and the rest of us don't have to discover them on our own.