You are right, I am jumping to conclusions based on what I'm reading between the lines: I presume this is not the first time the manager was shitty to OP since OP asked it in general terms how should he manage his manager, and I am also presuming the manager did not give satisfactory explanation for his refusal or offer a reasonable compromise(like "you can go, but you must never mention the company, our clients, our business etc).
I am horrified by the complete lack of empathy and emotional intelligence of such managers.
Won't OP just not hide such "silly" matters from the manager if whatever the matter is OP gets a slap on the wrist?
Is it indicative of good managerial skills that OP felt he should ask about the matter on the internet and not the manager himself?