Funny enough i had an almost identical piece like that in my pickup when i changed it, it was lodged to the side of the opening, out of sight initially. Never did figure where it came from... Sure it was metal though but it was a while ago.
I also had a few shards of plastic that had fallen off the dipstick at some point in the past. A worthwhile piece of maintenance for any TFSI owner, even if just for peace of mind.