I think you misunderstood each other, you meant a global method and Mr. Golick seems to have understood that you mean just another method in the controller or whatever.
Also, those are not really single-method classes, but single-method interfaces. Since you didn't give any arguments, I don't see how those two extra lines to define a class have any disadvantage in comparison to a global method, and having the framework define a interface to program to leaves more flexibility to the framework user than having the framework accept a method name or block instead. The instatiation of the class can be left to the framework user (in general, I don't know if this is the case here in particular) so that additional data can be attached, inheritance can be used (yes, inheritance has its problems, still it also has plenty of valid usage scenarios), methods broken down into smaller private methods etc. Also in Ruby there are no global methods like you would have in Python or C++, you always define a method of some class, even if it's in the top-level scope - files almost always correspond to individual classes so it would be pretty odd to have methods used here instead.
Also, those are not really single-method classes, but single-method interfaces. Since you didn't give any arguments, I don't see how those two extra lines to define a class have any disadvantage in comparison to a global method, and having the framework define a interface to program to leaves more flexibility to the framework user than having the framework accept a method name or block instead. The instatiation of the class can be left to the framework user (in general, I don't know if this is the case here in particular) so that additional data can be attached, inheritance can be used (yes, inheritance has its problems, still it also has plenty of valid usage scenarios), methods broken down into smaller private methods etc. Also in Ruby there are no global methods like you would have in Python or C++, you always define a method of some class, even if it's in the top-level scope - files almost always correspond to individual classes so it would be pretty odd to have methods used here instead.