Here is a page from a classic manga ドクタースランプ: https://i.stack.imgur.com/3llww.png In this chapter the professor shows Arale a camera than can look into the future.
In the bottom frame Arale says to him that this reminds her of ドラエモン, to which he replies 「あれはマンガ！」, and then the narrator says 「あんたもマンガだ！！」. What does the last phrase mean exactly? Is it a shortening of "you're in a manga too!", or does マンガ here mean "a manga character" (again in a shortened version perhaps?), or what? Is it just like how in English you can call a cartoon character a cartoon? (at least I think you can)