Also the possibility that people spreading the narrative that people are dishonestly spreading narratives to pump the stock.
My summary above is rough, and it's based on most of the information I've read about the situation. As always, there are voices on both sides for every single fact.
Time will tell how this all falls out, but right now there are a lot of finance firms grinding their teeth, which is a victory in itself.
Also, apparently Gamestop itself used the gain in stock price to settle some debts by being able to issue more stock to meet demand at the higher price, thus getting a cash infusion.