Source (Bluesky)
It’s also important to remember these models are trained by sampling (imitating aspects of) images they don’t have the rights to use directly.
So is basically every human artist. Basically any artist out there has seen tons of other art prior and draws on that observed corpus to influence their own output. If I commissioned you to draw something you didn't know what was, you'd go look up other depictions of that thing to get a basis for what you should be aiming at.
The way AI does it is similar, except that it's looked at way more examples than you but also doesn't have an understanding of what those things actually are beyond the examples themselves. That last bit is why it used to have so many problems with hands, and still often has problems with writing in the background or desk/table legs.