If this is true, then it wasn’t necessarily incorrect of him to say he transcribed it, as opposed to translated it, although he could’ve given Gilly credit for the assist in repeating it so that he remembered the fact.
Some have made the claim that the High Septon’s diary Gilly was reading from had already been transcribed by Sam, or that he may have done the transcription later on.
While there’s no denying that Gilly was the one to deliver the line in front of the audience, there is a bit of contention amongst Game of Thrones fans as to whether Samwell Tarly already knew that information.