iPhone 11 Backlash on the back or factory build

My iPhone 11 have backlash on the right side of the back.I bought it from mobile operator from our country Bulgaria for the standart price.They opened it infront of me and i removed the stickers and looked into it but i didnt saw this backlash because its really hard to see.And now this backlash makes me think the phone was opened in apple service to fix something inside of the phone or something.And i bought a opened iPhone.I go to the store 5 days after i bought it and ask why its like this , one from the girls that work here was having the same iPhone and color (black) she was have same backlash but on the diffrent side.She dont even know about this before now.So i m thinking is this normal or i should call apple for new iPhone ? Also on the photos it looks different because of the light or i dont know its not really that bigger in real life but its noticeable when you look close.