Sometimes, Stack Overflow itself compels some editors to make questionable changes to other user's language.
Here's what I think happened:
The user wanted to improve the formatting of the code by adding the missing four-space prefix on the first line. This suggestion could not be submitted because there is a six-character minimum limit for users with less than 2K reputation, so the user had to find something more to edit.
I've noticed this several times in the past, usually because the editor has mentioned it in the edit summary. I typically improve the edit by undoing the superfluous changes, as well as making other improvements if appropriate.