Big time backfire, if you ask me. His demeanor was such that he seemed to not care about the truth or understand the gravity of his testimony with a man's life on the line.
Again, pretending I am a juror (aren't we all??...lol), TTD neither came across as truthful nor as if he cared very much about accuracy.
I do not draw a conclusion from voice testimony. I believe he thought he heard DW speak and stopped what he was doing and went up to him and said "what?", but that does not mean DW said anything and wouldn't explain if it was an exclamation to himself or something else.
I am not saying the above facts are sinister by themselves, but when talking about the truthfulness of the TT driver he did impart some facts that will be part of the story.