Iroh's gaze flashed with rage, his chest heaving. He seemed to hesitate, and then he closed his eyes in resignation. Before Ryu could even react much, he released the Protector Spirit that the former was targeting and allowed Ryu to take it.
Ryu's fighting spirit dampened, but he didn't say anything. Even after defeating the four others, he was still not 100% confident in dealing with Iroh. The logistics of fighting in a team made it so that even if you were extraordinarily powerful, it was more important for you to fit in than display some outward showcase of strength.
Iroh had been greatly restricted in the battle because he not only had to cover for his teammates, but he also had to restrict the kind of attacks he used so that he only targeted Ryu and didn't harm his allies. He was quite confident in his own strength, but if he wanted to maximize the chances of his people and his Sect, the best thing to do was to avoid this battle.