Gay Ghost indeed. Aizawa only becomes a poltergeist when she's experiencing strong emotions. It looked like Aizawa was running away, when she got sucked into Kasumi. During the entire day, she was touching Micchi more and more. It looks like a mutual thing between them. Aizawa needs to be in her feelings to touch, and Micchi has to be open to it.
Aizawa saw Micchi getting closer to Kasumi, freaked out, and suddenly, her wish to be closer manifested into an unintended possession. She was so desperate to get her feelings across, Gay Ghost shenanigans.