Someone turned down my invitation for visit to our university for some private reasons. I am not sure what he meant by that. The situation is like he used to work for a company and there might be a conflict of interest if he come to our university to give a talk. But I specifically said to him that this should not be a problem since he is now retired and also that the talk is a purely academic one. Therefore, if it is because of the conflict of interest, there is nothing so private and he could just tell me straightly.
So I think maybe he really meant "personal reasons"? I have found this post on the forum. But I still want to confirm that I am not understanding it in a wrong way.