From my understanding, the Community user will approve or reject a suggested edit if there was a concurrent edit, or someone in the review queue clicked
Improve & Edit or
Reject & Edit.
I found a weird case just now, where the Community user apparently approved a suggested edit, while the suggested edit review log shows two users. There isn't an additional revision that could explain the concurrent editing.
The Community user approved, right?
... or didn't it?
As you can see, no concurrent edits.