I almost feel like the teacher opened the door that vigorously because he heard parts of what they were saying in there. "Thanks, it felt really good." "If it's Tokimiya, then... I don't mind." But that probably isn't it, they said way too much besides that.
Ive thought we would see they shopping this chapter... but i guess a storage room locked door cliche is also good.
Wonder if its just coincidence that shes getting along with him after he found out or if she was interested in him previously. I mean, she opened up to him about a lot of things nobody else knows.