That really depends on how you want to think about it.
For example, one of the OOP definitions is that “objects contain data and code”, and since it is more typical to define methods using multiple dispatch in Julia, which are not really “contained” in a value or a type, most things are not objects.
Or you can take the view that everything is an object. 
Personally, I would sidestep/ignore most OO concepts and as I do not find them helpful for programming Julia.