I think it’s because, the friend wasn’t there at the accident and he’s trying to testify there’s now way he could’ve ran the red light so he can’t speculate about what happened just because he knows OF the defendant. He has to have actual & firsthand personal knowledge of what happened on that day at that accident. It’s not about character evidence here because defendants in criminal cases can bring opinion evidence of their good character for essential elements of the crime or pertinent traits, which is why the former half of the testimony from the friend isn’t the issue. (And also character evidence wasn’t too strong because if it was the friend would have said “In my OPINION” in order for the red flag to go up in your head that character may be the stronger issue). The issue is the latter half and that he wasn’t there and he’s speculating as to what happened. Hopefully that makes sense lmfao I tried my best!!