As seen in Aronian vs Kramnik on day 3, the opening was e4 which Levon Aronian rarely plays. It later turned into the Berlin variation.
The article from FIDE says
Francesco Tristano, a classical and experimental pianist from Luxembourg, made the ceremonial first move for the round. By chance, it was in the game between Aronian and Kramnik, and he started with 1 e4, a move that Aronian almost never plays.
Why did FIDE allow Francesco Tristano to open for white in Chess Candidates tournament 2018? What if the person chooses a "relatively" bad opening like f3 or h3?