Altair and Vega did not discuss the Mona Lisa painting nor show off their knowledge of various artworks in the Louvre Museum. Both were accustomed to always acting humble and not attracting the attention of their friends.
Once they were happy with the museum tour and took notes and discussed the contents, they finally returned to their hotel. Altair and Vega asked Mr. Rhieu for permission to skip dinner because they had made a dinner appointment with Nicolae, Marion, and JM.
Mr. Rhieu finally agreed after Nicolae called him to make sure that the two students didn't lie and just made excuses to wander by themselves. No matter what, as the teacher, he was fully responsible for the safety of his students while they were in France.
If you read my other novel "Finding Stardust", you will know who caused the blackout in Paris. XD