فَتَلَقَّفَهُ الشَّيْخُ دُونَ الْحَدَثِ، وَاسْتَخْلَصَهُ عَلَى وَجْهِ الْجِدِّ لَا الْعَبَثِ
The elder snatched the dinar before the youth and took it for himself in earnest, not play.
Al-jidd / al-ʿabath contrasts seriousness with jest. Just after a poetic appeal for mutual compassion, the elder rushes to possess the coin, creating a sharp comic reversal.