Duryodhana points out the Pandava army to Dronacharya. The specific mention of Dhristadyumna (Drupada's son) is a deliberate attempt to agitate Drona. Drona had a long-standing feud with King Drupada. By highlighting that Drona’s own student is now leading the charge against him, Duryodhana is trying to ensure that Drona fights with personal vengeance rather than just professional duty.