Yes, I think that's most likely the explanation.
I'm not buying the "he's waiting for the 2020 elections" or "he can't release the docs because terrorist convictions will be overturned", explanations.
Right. POTUS is smart. Smarter than all his enemies. I doubt that he has trusted anyone outside his immediate family and I think hes kept some things to himself. Hes not going to let Mueller win.