I think you're a bit confused about how the Arduboy/Arduino works, while you can store data on it (via flashing and serial upload), it isn't a storage device that lets you drop files onto it, because it isn't intended to be one, and the operating system won't recognise it as such, because that would be really daft.
I don't own a modern Mac computer so I'm not sure exactly how it's handled (USB Serial ports, the manual suggests), but the Arduboy won't have any influence on the list of drives plugged into the computer and you won't find it there.
