Lexicon78,
I myself come from a family of control freaks and sometimes, they take me by surprise and ruin my day. I can think of two reasons for your boyfriends behavior:
One reason is that he may have grown up in a family where the parents wanted to know everything about him (they violated his boundaries). Thus, he may have decided to prevent that from happening to him again by being secretive.
And the second reason could be that his family may have been the type in which people do not comment on their plans or issues.