What does "sorted by method" mean? 

Use

This sort order sorts attributes by frequency of use and association in which the attributes are required for a certain object type.

Example of frequency of use

If the Sort by method option is selected for the Function object type, the attributes are sorted from top to bottom beginning with name, identifier, full name and definition. This assumes that these are the attributes used most frequently.

Example of association

If you use the Title and Link system attributes for an item, both are output one below the other because the Title attribute is used to uniquely identify the Link attribute. In alphanumeric sorting, these two attributes would be separated.