Hitting ESC doesn't make you end up in the main menu. That's why @Cap'n Bells asked. You end up... in the pause menu. Main menu is when you start the game and have the character selection in front of you.

It's probably just a misunderstanding.

My assumption would be that you were actually running a server and that's why the pause didn't work. But this is not the first time I read about this, although we're still waiting on a satisfying explanation if it really happened and if so, why.