Rilla never changed his boxing stance, hence although he was striking as an orthodox boxer he was still in his stated southpaw stance. Rilla is not a boxer, it takes a simple foot shuffle and body shift to change stances. Reading and comprehending your opponent is always the key to understanding the fight you are in. 

He does change stances to a peek-a-boo, after I hit him, which has it's merits and weaknesses. He is going to try to keep me at range with the stance (it is what it does, defense with punishing counters).