Gus: I, too, thought it was a sewn flat bag until I saw this notation on a photo the OP included:
View attachment 102094
which seems to indicate that the author, at least, intended that pattern to be turned. He also further re-enforces this with the instructions to cut two of the front and the back.
However If i crop the picture of the bag down, add a few hundred more pixels to it we can clearly see it is probably flat sewn unless their are directions for top stitching it in the pattern.
View attachment 102096
Leaving me with one of my many confused moments.
Just re-enforces what I have always said about bags: you gotta like it.
Still, I am not one to emulate:
as I, like the hatter, am
Mad Michael.