How was my design created and how can I group things

I had a custom illustration created that contains a scene with characters.
The final AI file doesnt have the characters each in their own layer where I can select them and isolate or do other thigns with them. Instead, its all one layer and everything is a path or compound path. Its like a bunch of small shapes that make up the image and different parts of the scene are scatter around.
It seems strange to me but I am able to work in photoshop and not in Illustrator.
Is this common? Doe the method have a name that i can search to find out more on it