The warrant officer class two, codenamed Person Seven, on Friday continued his evidence in the Federal Court, conceding that comments he made about the war hero to investigative journalist Chris Masters in a 2016 interview made him look small and petty.
Person Seven told Mr Masters in the interview that Mr Roberts-Smith was "not a bright bloke" and was "like a frilled-neck lizard", the defamation trial has previously been told.
Asked by Mr Roberts-Smith's counsel, Arthur Moses SC, if he used the six-hour conversation as an opportunity to "dump on" the former SAS corporal, the witness said "I gave Mr Masters my honest opinion as I saw it".
Person Seven told the court Masters approached him about doing an interview on his experiences in Afghanistan, and it was cleared with defence officials.
"There were certain topics that he hit on," the witness said.
Mr Roberts-Smith, 43, is suing The Age, The Sydney Morning Herald and The Canberra Times over reports claiming he committed war crimes and murders in Afghanistan between 2006 and 2012.
He denies all the claims against him, while the media outlets argue they are true.
Person Seven has previously told the court he watched war veteran Mr Roberts-Smith attack an unarmed and frightened Afghan prisoner, relentlessly bully a comrade and threaten to strangle a man with his bare hands.
The witness has also said he was told by a soldier, dubbed Person Four, that Mr Roberts-Smith kicked an unarmed Afghan prisoner off a cliff in Darwan in 2012.
The SAS member was one of two anonymous sources who appeared on 60 Minutes in 2019 in breach of Australian Defence policy, the trial has been told.
He has rejected defence claims at the trial that he went to the media motivated by jealousy in a bid to disparage Mr Roberts-Smith's reputation.
The trial continues.
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