I genuinely believe that he's a creature that can use its goo to shapeshift into any object or living being.

Probably insecure and shapeshifted into an apple to appear more adorable and less 'scary'

Those 'family members' he has that steve totally hasn't eaten are either probably actual living apples or the same species as Ethan.

And to explain the red parts and the leaf and stem he still has, due to being in this 'apple' form for so long, it takes a while for these feature to go away!

This is just a theory! I don't know if he's actually a creature or alien of some sorts T^T

Consider this as concept/fan art for @BOXZEE :]