So it's been a while since I saw that scene but here is what I remember. Initially, she busts Otaku in the locker room. I think she spread a bunch of women's clothes around him to make it look even more incriminating. However, she goes way beyond what is necessary to get him in trouble, and gives him a footjob. The comments she makes while doing it certainly seemed to suggest she was kind of getting a kick out of it, as I recall. I think it was in the spirit of like, oh look you are so gross you like that what a dirty pig etc. (while continuing to get him off) - I myself thought at the time that this was foreshadowing and maybe the author was planning to build in the possibility of Otaku getting into a relationship with her eventually.
So, you could just have followed the same logic path I did, or hell maybe there is some content like that in there and I either didn't reach it or am forgetting about it, but I can 100% see how you might come to that conclusion.