But the office is closed!
Don't forget that sound can travel through the thickness of doors, and even through some sorts of wall. The sound is attenuated (weakened) but here something else comes into play...
The ear's sensitivity is 'logarithmic'. This implies that it is disproportionately sensitive to very weak sounds. So although the sound intensity might fall by a factor of 1000 as the sound passes through the material of the door, it may still be audible.