IMPORTANT: At no time should your friend ever admit to disobeying the stop sign, to either the prosecutor or the officer. If they ask your friend this question, your friend should answer "I have no comment about that at this time." The only exception is if your friend takes the witness stand under oath (in this case they WOULD have to answer all questions honestly). However your friend has the right not to testify against themselves and does not have to take the witness stand, and if not on the witness stand under oath, they do not have to answer any questions about this.
I would say yes, this portion of the officers notes should probably raise enough doubt to get the charge dropped.
So during trial, the officer will testify and prosecutor will ask them questions to clarify.
Your friend will then get to cross-examine the officer. This is NOT the time for your friend to give their version of events, but this is the time to question the officer on their testimony and their notes. So your friend would ask lots of questions concerning this particular notation in the notebook.