I've gotten several complaints about this, it's seems like it's checked by default for some reason. Please make sure to uncheck it if you create a community, ESPECIALLY if you make multiple in a short period of time.
Edit: this has been fixed piefed dev, but please make sure it is unchecked
Do I need to create a user account here to create a new community here?
Yes. You need to create a fedinsfw.app account, and then create a community.
But once you've created a community, you can make your reddthat.com account a moderator.
I'm not sure if lemmy users can make piefed communities, but if they can, I haven't put any restrictions on that.