Welcoome to this forum Morettina!
Some ortho's like to mark the centre of the archwire with a pen or a piece of metal, to help them centre the archwire when they're putting them in place.
I'm sure the extra piece of metal you can see was there all the time and it sounds exactly like how some of our flexible archwires are. These are the archwires used in early treatment and often they slide too much, so these 'tubes' make it easier to keep an eye on them at adjustment time.
Good luck with your progress! :thumb: