It's possible that happened but does it make sense? You have all that steel sitting offshore and the same groups of people involved in secretly obtaining it. Plus dealing with the U-boat situation to move it twice across the Atlantic when you're perfectly able to use in in Englandfor your own production.
Argentina remained pro Germanythrough the entire war and sheltered the Nazis after the war so what any of them say or claim is suspect.
I don't think there's any proof either way. Testing didn't show it came from the Graf Spee but it didn't eliminate it either nor show it came from the US or England.