It was just to prove that you could use this syntax for a relation - similar to what is done in https://github.com/cakephp/cakephp/pull/2292/files#diff-502b28a0e9572a5101fbba8a5d52a17fR274 

But I agree with the multiple syntaxes, I remember that also confused me a bit when I first got into cake. (From a users' perspective). I will remove the string-only option.