Have seen this idea demoed before....curves are not that hard...I started doing drunkards path...now that's a curve!, but after one or two....you get the feel of it...like he said....slow stitching us the KEY......
Now...as he was cutting those gentle curves from those strips then sewing them..I was thinking...why not just lay two strips down - right sides facing though,and sew the curve, then cut 1/4" away? or sew both edges in a curve then just cut straight line between them........and open them up? I am not near my sewing cave...just thinking...would that work? May have to go down later and try.
And....why do demos sew standing up...watching that makes me nervous......