Its the distance from you to the person who wrote the post. However if the person has not given the exact ( or true) coordinates, the distance is not real. You might have given your coords in the initial set up of your account.
BTW if you click on the persons name, you can view their public profile and find their coords ( and other stuff too).
I have not given my exact coords for fear some nefarious characters might use this info and google maps to find your house and come knocking at your door when you are not home
Cheers
Bart