Setting the default for an attribute in an order level setting is an option you can set up. If you go to a Product Attribute, you will see a checkbox that says "Set Attribute Default in Order Level Settings"
Checking this box will allow you to set the default in the Order Level Settings instead of setting it on this attribute page. Once you select that box, on the order page you will now set the default for that attribute in the Order Level Settings. So whichever option you change that attribute to, all of the products that you enter into the order will now show up with that attribute as the default.
If you uncheck the box that says " Set Attribute Default in Order Level Setting", then your attribute will go off of whichever default is select on the attribute page.