No, it's definitely a dark pattern. Everything about the page suggests that pressing the "generate 4 images" button will generate four images. And then it doesn't and tries to lever that anticipation to get a sign-in. It ends up just making users angry.

If you need a sign-in, e.g. to prevent abuse, you could start by explaining that a sign-in is required and why. At least then people won't be angry when they are ambushed by it

Ok, agree about that. Just did not have time to polish the details. It's not intentional. I've added login to the site, after nearly going bankrupt for offering free generations. The UI needs an update.

It's absolutely not transparent. Showing an active "start process" button that leads to a sign up / login form isntead of starting the process is absolutely not what users want or expect.

I think this is the very definition of baiting.