I have seen this on a lot of gravel bikes (dropped drive-side chainstay.)
Possibly it is because it gains an inch or so from the base of the chainstay to where it clears the ring, to where it passes the tire, so the angle outward to clear the wider tire isn't so dramatic. When I look at the posted photo, it seems the chainring almost overlaps the tire--maybe 3/8 inch clearance---on a direct line from the BB to the axle (traditional straight chainstay._
With the angled chainstay, it seems that the chainstay has more than an inch clearance (radially from BB to intersection of tire and chainstay) which means the chainstay can make a slightly gentler outward bend. Makes sense to me.