There are 2 parts to this, IMO.
One - there are plenty of end users that will complain about anything a lot regardless of being right or wrong. Those could be external contaminates not rust.
Two - AFAIK, every stainless steel will change based on reactions with external elements. Some, see#1, would consider it rust which in fact it is not.
I know a manufacturer who makes 100% of their work in stainless and they said that any stainless alloy which is exposed to outdoors and extremities needs to be treated to maintain its looks.
Another thing is that CT stainless alloy is somewhat magnetic (see TSportline 'test')
In any case, would love to see this addressed and explained by metallurgy expert and/or Tesla.