Not sure what I'm looking at. Have you tried pulling it out? Does it look like it's just wedge in between the rim and the tire? Might have just gotten stuck in between when the tire was mounted. Or is the string embedded in the tire sidewall?
It was probably debris that got molded out through the tire if it's in the sidewall. There are so many layers that its probably not an issue. I would register/document it with pirelli just in case you need it replaced. These are beefy run flat sidewalls.
if it's actually coming through the sidewall,ask dealer to replace the tire. i would not want anything coming out of a tire on a vehicle that can go 200+mph.
at minimum,tire bead should be popped off the rim at those locations for a visual check. based on what i can see in photos,it looks more like something is sandwiched between the bead and the rim.
It's hard to tell from the picture but could it be from when the car was washed and maybe the wash mit strings got caught in the crack somehow? I have noticed on occasion my wash mit gets wedged between the body trim and I have to pull out the small fibers later.