My cat hides in a special spot INSIDE the filing cabinet when someone else comes over. He hates men so, if he hears a woman's voice he is okay but a man's voice and he is gone.

Personally, this is not bad for me because the landlord doesn't know about him.

I would say if the behavior has always been there and is consistent, there is no need to worry. The worst is when they start changing their behavior. If you don't notice physical signs (i.e. vomiting, whimpering, limping) then I would just attribute it to him liking that spot. If you really don't want him under there then you might just need to close it off completely. However, if he likes tight, enclosed spaces, then he might just find another spot.