Found this string like poking out of my butt after BBL

About a week post op I pulled this out of my lower left butt cheek. When I asked to speak to the doctor about I basically didn't get a phone call back and answer from the nurse that it's flesh of fat? But how could that be if he didn't cut me there, at least he didnt mention he would. Any way I pulled it out and it started to bleed. I covered it with band aid and it has healed by now. I am just curious and still a bit worried about it as another one of his patients experienced the same thing.