That looks like the hidden "__MACOSX" folder that OSX includes when performing the normal "Archive as" function. That hidden resource folder can't exist in a valid ePub (and still pass validation, anyway). This is one time where doing it "from scratch" is biting you in the ass. Don't create an "archive," create a zip file with the "zip" command—if you insist on doing it from scratch. But I recommend using pdurrant's tool for easily zipping/unzipping epubs
properly on OSX, instead. There are special considerations when creating an ePub package (the mimetype file must be first and uncompressed).
Your validator is complaining that the files (that start with "._") in the hidden __MAXOSX folder are NOT declared in the opf. And they shouldn't
be; because the hidden __MACOSX folder shouldn't be in the ePub package in the first place.