It's a 2-G handy-box... hence no mud ring.
BTW, the original YouTube that I linked to was edited not so long thereafter.
In the original 'Tube he was working with blue latex gloves on an obviously hot receptacle.
That 90 second sequence is now entirely missing.
For the effort expended, I would've installed GFCIs.
As for his tradecraft, It's below what I would expect of myself. I'm more than willing to slow down for old work... and price it accordingly.
There are Romex connectors that fit 1/2" metallic KOs which can be installed afterwards -- and from inside the box going outwards. They are not expensive. Using them would've entirely eliminated the need to hack up the plaster.
The plaster damage at the southwest was no doubt caused by pushing the expanded metal back into the wall instead of cutting it clean. I'd consider that embarrassing collateral damage.
I can see that he gave up on using a 2-G old work box. (Carlon - blue) because the expanded metal and the surface tabs (@ Carlon facing) made it problematic. So I agree with his selection of a 2-G handy-box.
A tip for anyone cutting into old work:https://www.youtube.com/watch?v=WPLlZ1JGB9Q
Blue tape makes for a superior layout surface... much easier to define ones cutting lines... and able to double check for plumb and true.
For such low cut-ins I prefer to use a traditional carpenter's square during the layout: its wide side is EXACTLY perfect for the width of the common 1-G cut-in box. I merely double check to see if the square is plumb and the floor is level. It's much easier to trace without shifting position (of the cut-in box being traced) when a carpenter's square is resting on the (level) floor.