Just guessing, but I’d say the trim cover departed the aircraft at some point.
The Speed tape will keep the airflow smooth until it gets back to a maintenance base. You don’t ground an aircraft for that.
In my time, I’ve seen some aircraft flying that were “covered” in the stuff. I was on one of the last United 727’s in service, that had speed tape and orange tags all over the place. They weren’t going to spend any money fixing minor problems on an aircraft that was going to be retired in two weeks.
That’s what I thought, too. The small piece of metallic covering had been lost.