By default, the top staff is for the right hand and the bottom staff is for the left hand. Those brackets are used to indicate that notes should be played with the other hand. This seems to be indicating that you should split those notes between the hands, playing one note with each thumb.
This seems really strange, but I get why the editor suggests it. If we try to play all of the notes in the top staff with the right hand, it's very awkward to play the C/Bb pair near the end of the measure while also holding the G with our fourth finger. If we try to play both pairs of dyads with the left hand, we run into a pickle with the left hand fingers.
Still, I think the fingerings are too bizarre to use. I would suggest playing the first dyads (C/E) with the right hand, and the second ones (C/Bb) with the left.