With user created stories, the authors can choose whether their choices use Gems or not. I’m sure Episode wouldn’t put Gems in user’s stories without permission as it should be the writer’s decision. With the “support author” part, it’s a way of paying them. As in, if you’re 18 or over, you can get paid through your Episode stories. So, in a way, you are supporting them.
To be honest, gem choices are so annoying (especially in Episode official stories) but if it will get the user money then it’s worth it for them.