Got to love the way the Portuguese organise their national airline. I suspect the crew couldn't be bothered to move the curtain. It has happened to me when I had a business ticket and only got fixed when I told the FA that I would be offloading myself.

What is for sure is that when your BP was printed row 5 was business class. The data on the BP is not manually created.

I would suggest a different tact. Complain to TAP, sending a copy of your boarding pass, that you were on a business class flight but you were refused business service because the curtain was in the wrong place. Tell them you felt that you were downgraded by the crew and ask for compensation. Nothing to lose.