Olly did not take Divination. Olly did not like Divination, which would be why he did not take it. So when he entered the tea room his thoughts were not on using it for Divination purposes. He did not think that was a requirement of the room. It was there and open for all students. There were no rules on how it had to be used. So he was just going to use it to make some tea. Because he liked tea (unlike Divination).

Olly had sent an invitation to Ava to meet him there for tea, because it had been a while since he had hung out with her. Sure he'd seen her around but he wanted to actually hang out and catch up. She was his friend, after all. And for her, he was willing to walk up all those flights of stairs. It seemed that he had arrived first, which he didn't mind. He'd made a point of not being late and it seemed that instead he had arrived just a bit early. That was okay, though. It only meant he had time to start brewing the tea before she arrived.