It's not marked correct or incorrect by AI. They have to set the possibilities manually and define the errors. One of the volunteers who act as a go-between once posted all of the manual work they have to do to define what is right or wrong. It looked crazy making and explains why duolingo is so full of errors. They made a mistake, not a big deal. However, the really frustrating part is that this was reported at least a year ago and as of today it is still incorrect. This is the case for most of duolingo regardless of whether you pay or not.
Al (contraction of a el) or a los is used following jugar - check out this explanation. https://www.spanishdict.com/answers/188968/why-the-al-in-for-example-quiero-jugar-al-tenis
I (like two posters below) am also confused and just guessing on when to use an article in front of the noun. I went to spanishdict.com since it has been referred to a number of times in these discussion pages and found that there seems to be no hard and fast rule but rather a number of guidelines. Here's an article that cleared things up a little for me. Hope it helps. https://www.spanishdict.com/guide/using-the-definite-article-in-spanish