difference between Data Element & _satellite.setVar

Yes, that is setting the data element.

Basically, you have two possibilities of defining data elements that are mutually exclusive

1. using the Launch UX which will always require some kind of data element type (which is important, see caveat)
2. using custom code like you have done here

Both types of data element can be referred to in extension interfaces through the percent syntax e.g., %my data element%

The big caveat though is

• data elements set through setVar are not accessible through a UX data element with the same name.
  In other words: you cannot declare the data element via UX and then assign a value later through setVar
• If you need to write custom code to define the value of a data element, use a Custom Code data element instead