Duryodhana says to Drona: "O teacher, look at this great army of the sons of Pandu, arranged in formation by your own intelligent student, the son of Drupada." Every word here is chosen with care. There is a calculated sting hidden in this polite address.
Dhrishtadyumna, the son of King Drupada, is the commander of the Pandava army. He also happens to be Drona's former student. Drupada and Drona had an old rivalry. By pointing this out, Duryodhana is reminding Drona: the student you trained is now leading the army against you. Let that sharpen your resolve.
This is political maneuvering on the eve of battle. Duryodhana understood that wars are won not only by swords but by the fire in a warrior's heart. He is trying to kindle anger in Drona before the first arrow flies.