Are you referring to a dictionary of word definitions? The kind that is structured as a list of words, ordered lexicographically? Where is the categorization in that?
He's referring to the dictionary definition of the word "sort".
Dictionary.com has it as "to arrange according to sort, kind, or class; separate into sorts; classify". I looked it up in the OED too -- mostly because we have one and I don't get enough excuses to use its nifty little magnifying glass -- and it also supports the notion that it means by category, not by order. The general verb definition is "to arrange things according to kind or quality", and there's a separate definition for software: "sort: Computers: the action of arranging items of data in a prescribed sequence".
