You made it sound like it's a hobby project not ready for production — where do you see that in the README? Calling it a "WorkOS clone" because they mention it is an alternative also isn't fair — even if it solves the same problem! The fact that they previously worked on something else also doesn't work as an argument, not sure why you would present it as such.

Just be nice to each other, even when they're your competitors! It's not so hard.