Why are the contractors leaving lambs wool fibers in my floor finish?
They are using new clothes on final finishes.  New wool will shed maybe the first 10-20 times you use it and for finish coats I have only used older clothes or microfiber.  They could also be buffing a little too soon and this will definitely cause more wool to pull out.   I would hit the areas with wool with 320 grit sandpaper or just leave them in there and they will work their way out with more drying and usage.