:Agree. Although I don't know much about the standard, but from the text:  

 ::* The OpenDocument Format 1.0-1.1 specifications refer to 'ZIP' files but do not reference a standard which describes the zip file format. 

 :The specifications just "refer to" ZIP which is not supposed to be included in the spec. It is hardly to say it's a related criticism to ODF IMO. Similarly, it is hardly to say a book is bad just because it doesn't give a clear picture of what it refers to. It's acceptable to leave the ZIP unspecified/undefined. -