This has been discussed in other gen5 threads. As I recall, this is not rust but discoloration caused by residue/contamination left on the metal prior to painting. Simply a cosmetic issue; no need to be alarmed.
From @daisy555 picture in the link, looks like the same sort of pre-paint debris present: [Apologies for misplaced image: iPhone IOS 26.1 is driving me spare]
