Keep in mind that he really does not need any proof to call the police and ask that they investigate. In order for your brother to be charged with a crime, the state would effectively have to prove that at the time of the report he KNEW that the motorcycle was not stolen. Being in error is generally not going to be actionable. And, as Quincy indicated, the state is not going to be too interested in chilling interest in people reporting crimes by going after people who MAY have been using the system to one up a family member.
The matter was resolved in your favor without any apparent harm. It's annoying, but hardly seems actionable at this point.