|It is usually a good thing to be regarded as a promising employee, but not in this case. However, trying to change the behavior of this department head may be trying indeed. You can certainly tell him that you do not appreciate being misquoted, but he would probably misquote you on that, too.
Fortunately, there are some other steps that are more likely to help in this situation and change his behavior. The first is to provide your manager with a brief summary of your meetings with this individual. You should do this as soon after any such meetings as possible, preferably in writing. The easiest way is to send an email, and you can copy the misquoting manager.
A second approach that can also help is to send the distorting department head a self-serving letter after your meetings with him. This type of letter would summarize your discussion and leave no room for his embellishment. You should send a copy of this to your manager.
Since you are dealing with a documented distorter, it is important for you to document your conversations with him.