That coordinate that's being shown is for the place where the user clicked.

The map has no option to show all the coordinates of a polygon, there could potentially be too many. However, you could have a field with the concatenation of all the coordinates and map that field to the description. Keep in mind that, if there are too many coordinates, it might be confusing for users to display that information in such a small popup.

It would probably be best to have that info outside the map, you could use a table list to display all the coordinates, for example.