Okay, Without knowing all the details the news report says the plane was half full & the couple did not understand why they could not sit where they wanted. Also said they tried to move themselves several times.
Pretty sure repeated attempts to occupy seats that were not yours would fall under "not following crew instructions". I am pretty sure they were told there was a charge for the E+ seats. I also doubt they were not offered to purchase those seats by a FA. Those announcements are always made pre departure when E+ has vacancy.
If I caught someone trying to shoplift in my store, I would have them removed also...