If I had to take a guess I believe he means that he is a very smart intelligent history teacher. He is familiar to the topic of history and knows enough to be a teacher, and a very good one at that. I hope this answer helped and I'm sorry if it didn't.
When the guide calls Colin a "brilliant history scholar," he means a British student with vast knowledge of the Magna Carta.
Explanation:
In "Magna Carta Meltdown" by Mary Clare Gordon, the guide uses "brilliant history scholar" as a figure of speech to describe Colin and his explanation of British history, all while also referring to the role of the British people in gaining their freedom.
