"Their hearts are distracted," meaning: heedless.
Muhammad said: The meaning is: they listened to it while playing, with their hearts being distracted.
﴿لاهية قُلُوبهم﴾ أَيْ: غَافِلَةً.
قَالَ مُحَمَّدٌ: الْمَعْنَى: اسْتَمَعُوهُ لَاعِبِينَ لَاهِيَةً قُلُوبُهُمْ.