That, too, looks about right, so it’s pretty much got to be the wrong file. It may have gotten cached or not overwritten or something.
I’d try again with a different filename, e.g.
rm cocos2d-forum-2015-05-01-041307.tar.gz
tar -cvzf cocos2d-forum-2015-05-01-041307-v2.tar.gz -C cocos2d-forum-2015-05-01-041307 .