|In essence, your boss is saying that if you need to think carefully about a major decision, you are not someone who should be promoted. That's rather ironic in light of the fact that most senior positions call for some rather deliberative thinking. |
It would have been more businesslike and professional for him to meet with you to discuss the position in more detail, rather than unilaterally rescinding an offer that never had a deadline associated with it.
By thinking carefully about the next rung on the ladder, rather than instantly grabbing it, you are actually making the right move, even if it is not a move at all. Many people are so smitten with the notion of being promoted that they ignore what the promotion truly entails. In such cases, the promotion is better described as a commotion.
In terms of the bigger picture, the fact that your boss had no qualms about unilaterally pulling the offer most likely means that he has no qualms about pulling a few other stunts as well.