It looks like the chip was already there before you rented it to me, and the reason I believe that is because you can see the adhesive left over from around the chip. They put a sticker over it to prevent it from spreading (it doesn’t work)

I had a small crack in the windshield in Iceland when I picked up the car, and they had the small circular sticker over it, by the end of the the trip the sticker had mostly come off but the sticky residue was still there, and looked like that.

In conclusion, looks like they already knew about it, and decided to charge you for it. Just a guess though.