Dust in rear camera Iphone X

Here i bought an Iphone X for my friend, the second day he found dust in the rear camera which we all know that Iphone X is waterproof. Therefore, we send in the Iphone X to apple service store, the customer care told me that they will disassemble my Iphone X and swap the dust. Honestly , a brand new phone has dust inside and you gonna disassemble it and return to me. That not what i expected. I has the thought that the Iphone X is not waterproofing which dust could get into it so what it resistant actually? Does anyone face the same issue ? Please advice. This is the result from Malaysia Apple Store service center and the result from Singapore Apple store. They just trying to ignore me that made me feel suck to Apple. Foremost, it a gift to someone else it make me feel awkward when i had been told cant replace a new one!