Good morning everyone. Do these two words both mean Albanian and why the difference? Is it regional? Does one tend to be used in some parts of the country while the other are used in others?
No, it's not regional, it's a matter of historical period. In the past, in the late Middle Ages, when they first appeared, it used to be Αλβανίτες and the adjective αλβανίτικος. As the centuries passed the type Αρβανίτες predominated.