Question about what Duolingo says checkmate is?

In the chess lessons, Duolingo says it’s checkmate when a piece is one square away from capturing the king. For example, if the queen is in the square right next to the king, it’s calling it checkmate. How can it be checkmate when the king can capture the queen in the next move? Is the other player not allowed to capture a piece if that is the only move to continue the game? I’m confused.