My parents had a disagreement, nothing serious, not even raised voices, but their German Shepherd sensed the tension and moved between them to sit in front of my mother with his head cocked staring at my stepfather. The rest of the day he stayed very close to mother.
Funny thing is they seldom disagreed and never got very heated when they did but that day the dog noticed some tension, did not like it and made them aware that he was there to defend and protect his mistress.
Our German Shepherd does funny things like that as well. I personally believe the guarding instinct is so powerful that they like to guard and protect even when not necessarily needed. It is obvious that tension was new to this dog and he didn’t know what to do? So, he guarded your Mom and stuck to her like glue. In his mind... just to make sure that she was okay. Good doggie!! (I bet your step-Dad watched his step for a few days, huh?!)