Oh cuz belly buttons come with umbilical cords and with how Adam and Eve were "created" no cord was involved .so what your getting at is that man is contradicting itself by painting there creators creation In There own image
That painting is very old so you can assume that people didn't really know the thing with belly buttons and cords so they just drew them based on how THEIR body was constructed.
It actually possible that God created them with bellybuttons. We do not know. We can however assume that if the Biblical narrative is true then God must have created the world as if it had experienced many things, or else science wouldn't keep finding things "older" than the Bible says the planet is. It stands then to reason he might create Adam and Eve as though they had been born, and therefore they would have bellybuttons.
That's what your main concern is?