Amsterdam (Schiphol) has certainly become busier than Frankfurt, and has remained so since 2016 (so this quiz was probably created before this happened, also in 2016), however I doubt that Amsterdam has more passengers than Moscow. Moscow has 3 large airports: Sheremetyevo, Domodedovo and Vnukovo. Sheremetyevo alone accounts for 50 million passengers.
Amsterdam is bigger than both Frankfurt and Moscow.