Yes, they are both privacy friendly OS with microG preinstalled to replace Google services. But they’re not based on the same project : IodéOS is based on LineageOS (like /e/OS) while Calyx uses AOSP.
It’s not a huge difference but in my experience after switching from Calyx to Iodé, some applications wouldn’t work anymore, mainly banking apps.
To be precise, it is The Satanic Temple, not to be confused with the Church of Satan. They do a lot for civil rights in the US