I'd take the job without further debate, and start looking for a new job if you really don't like the new position.
I can imagine some reasons why your boss was mad. It's a small company, and you are being offered a position with greater responsibility. You may be the only person that's viewed as suitable for the position. It's quite possible, at least based on what you've said, that you are being groomed for bigger and better things. If that's true, your refusing to accept the position may be seen as an insult. This is speculation, but something to think about.