Service rejected due to slight rust at screws?

I had a very unpleasant experience in Apple Store Singapore Orchard Rd. The screen of my IPhone 13 Pro is showing only green lines. The Genius Bar staff is rejecting to repair because as the screws are rusty, and they tell that this is an indicator for water damage. The phone was never in water. I just had it with me when doing sports. And the last time has been a while. That is very frustrating and not acceptable. I’m not expecting that it should be repaired for free. Just the explanation “suspected” water damage is frustrating, especially in a country with very high humidity.