I read your thread in Ask The Rules Team; it's very likely that whoever brought this up to you was being - uh - let's say oversensitive.
I live in a very humid area (not as bad as Florida - it's a bit legendary there) where foil cards left unprotected, and sometimes even in sleeves or binders, will naturally curve over time. This means when you play them, some believe that the curvature makes it easier for them to get "cut into", and will create a gap in your deck that you can see so you can tell where the cards are.
I've personally never had a serious problem with this and can tell you from experience that you can usually straighten these curved cards by leaving them in a heavy book overnight, if you're worried about it. Most likely, you're fine.