It clearly doesn't use minimax, since it doesn't play the best move for black in the critical line, leading to a mate in 5 instead if a mate in 6. Best line is

It clearly doesn't use minimax, since it doesn't play the best move for black in the critical line, leading to a mate in 5 instead if a mate in 6. Best line is N4 N5, Nx6+ K7, R4 N3+!, K2 N5, N8! Kx8, Rx5#. The site has black instead play Kx6 on the third move, allowing a faster mate.