Since Roy was carrying out a blockade mission, he didn't get too close to Argus. Instead, he stationed himself on a satellite outside Argus and divided the Burning Legion demons he brought into dozens of groups, arranging them in an encirclement outside Argus on starships.
When the starships of the Burning Legion appeared, the eredar on the ground of Argus naturally saw them. The people led by Archimonde and Kil'jaeden were already preparing to welcome the arrival of the Burning Legion, especially Kil'jaeden. He, who had been indecisive at first, finally put aside his hesitation after discovering the appearance of the Burning Legion and planned to submit completely to Sargeras.
At this moment, the eredar society had already been divided into two sides. Those who didn't want to join the Burning Legion had basically all gathered around the prophet Velen. When Velen learned of the appearance of the Burning Legion starships, he realized that he had to act quickly.