Looking at the picture, it appears that OSB sheathing was installed at the corners and mid sections of the framing to meet the building codes for lateral stablity and ridgidness as required by the AHJ.
The black sheathing I see is most likely a 1/2" regular cellulosic fiberboard sheathing.
I call this the Connecticut Framing, where 30 years ago it was used as a backerboard for siding. Thereafter in Northern Maine, people thought the vaporseal had to be on the exterior. Wrong answer. Vapor barrier goes on the warm side of the wall.
This picture depicts as cheap a method of building today as there is. Meets Code, yes.
Remembe Code is the minimum standard allow. Does that not tell you that people are there to make a quick buck, and will only provide what meets the minimum and nothing more. ?
Don’t we live in an ethical world!!! ha. ha.