Maybe he didn't design this for phonologists? I doubt anyone else has too much use for intra-word diffs.
The original sentence is: "He went to the stoar." Person A sends this to person B for review. While Person B is reviewing this, Person A changes the sentence to "Bill went to the stoar.". Then, Person B sends back the spelling correction; "He went to the store.".
If the sentence translated to one line for `diff` to work on, this would be a merge conflict. If each word was its own line, this would merge cleanly.