Both are different!
In the object list you have the all objects in your current scene.
Object variables are variables added by edition of your object in this list.
(right click on an object then “Edit object variables”)
On the scene you drag and drop one object, one object on scene is called instance.
An instance is one or many duplication of your original object.
If you have one object “Player” in object list, and two “Player” on scene, so you have two instances of “Player”.
Then when you click on an instance you can edit the values of the selected instance, position, width,
At the bottom you see the “Instance variables” section.
If you have setup an object variable on your object the variable and the value will be shown in this section.
This variable object can be override, if you edit the value of the variable in this section, the value go to italic, this mean you have write over the object variable, and this value is now effective only on the instance selected.
If you click on a second instance, you will see the object variable, but not the value edited on the other instance