I thought it would be easier too..except there are 4 point to match instead of 1. With a bias cut it is easy to get just a little out of whack or a less than perfect seam on each one so that when the block is squared it makes different size points. A great deal of starch helps but still as each block goes together side by side it's difficult...Also when the two 4" ones are put together, split and pressed they are slightly smaller than the 5 " block so that has to be wiggled in..the direction it is pressed has a lot to do with the size too...I coulda/shoulda used sashing as I have seen and liked but didn't like the look for this one.
I did watch the video...at least a dozen time...I'd think I missed something and so I'd go watch it again...It looked so easy. I'm sure for those with lots of experience it would be much easier. My block were square so it was no problem lining them up...just the rounded part.
Here's a pic to illustrate..