That isn't proof. It isn't even evidence, because there is nothing stating that the words "could not" be translated. To me, it's a simpler explanation that specific words originally spoken in Aramaic (as opposed to Greek) were preserved in Aramaic precisely because they were unusual.
But there was a study done before on this topic from another forum.
Anyways, it was an independent theological reseach done that claimed, the words in Aramaic were hard for the Greeks to translate, but the Greek could be translated by Aramaic because Aramaic has every word that the Greek has PLUS MORE.
Seems rather clear and obvious at that point why those Aramaic Words [Spoken] by Peter, [Written] by Mark, (we know this information from Papias, one of the Apostle John's Disciples) ...were not translated, because Mark's Greek Language had [no words] in their own Language to apply.