Is this his Sunflower quilt - I think he called it Red Diamonds?
I made this quilt ages ago. There are no Y seams in this quilt as you're sewing the diamonds into rows (as if the blocks were on point).
You DO have to be careful of bias edges, and of lining up the pieces correctly so when you unfold them, they're aligned properly. It's the same rules as when sewing triangles (not 45 degrees) together...you have to offset your seams.
(the same way when joining strips for binding...you want a nice straight edge on the top and bottom)
eta: most of the tutorials out there seem to be about sewing diamonds into a LeMoyne star.
Here's one that's sewing them into strips:
http://urban-patchwork.com/?p=996