Yes, I'm assuming his story is accurate. Otherwise we are just debating hypotheticals.
I think that if you conclude that the company is not for you, and you feel that the interviewers have been less-than-nice, you are saving everyone otherwise-wasted-time by leaving early. I don't see how you are under any obligation to go through the motions in a process where you do not want a successful outcome. It's not rude to realize the company is not a good fit for you and save time.
In fact, why should any interviewer be offended with a candidate who has made this decision and leaves early? They've already decided they will not accept any offer from you. The only reason to be offended is if you cannot fathom than anyone would not want to work for you.
You're absolutely spot on. The reality is that candidates ending interviews prematurely is incredibly rare. If it happens then something has failed within your interview process. The only way you will know this is if the candidate clearly explains his reasoning for ending prematurely.
I think that if you conclude that the company is not for you, and you feel that the interviewers have been less-than-nice, you are saving everyone otherwise-wasted-time by leaving early. I don't see how you are under any obligation to go through the motions in a process where you do not want a successful outcome. It's not rude to realize the company is not a good fit for you and save time.
In fact, why should any interviewer be offended with a candidate who has made this decision and leaves early? They've already decided they will not accept any offer from you. The only reason to be offended is if you cannot fathom than anyone would not want to work for you.