Your manager could have just as easily thanked you for making him look good. After all, you are a member of his team, and it is widely believed that strong managers hire strong employees.
Part of this issue obviously depends on the way that you elaborated on his answer. For example, if you opened by implying that your manager is some sort of a dim bulb, then his reaction is not altogether surprising.
The more likely case is that your manager is feeling insecure and may sense that you are going to leap over him. The problem in this scenario is that he may consciously or unconsciously try to place you in situations in which your goals, needs, and motivations are not being met, and in which you ultimately fail.
You should meet with your manager and tell him that you sense a drop in communication with him lately, and then let him talk. If he is upset with your comments at the meeting, emphasize the fact that you simply provided information on a question from senior management. Neither he nor the department would have looked better if all of you sat there and stared blankly at the senior manager. As for the future, if he expects you and your staff to "dumb down" in these types of situations, then it may be downright dumb to remain in this department.
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