Thanks for the quick reply Jason. It looks like this is a macOS(Sierra) issue with the Archive Utility that is the default tool to unzip. There’s a preference in the default settings that ‘Keep expanding if possible’.
The utility can read the packed format of the .bin file after it has been extracted and expands it in turn producing a folder of the embedded linux files then automatically removes the bin file that I wanted. You can either turn that option off in the preferences. Or I just opted to use the cli unzip command.