This is a great pattern. Seamless from hood to sleeve ends. The creation of the hood, starting with ‘Judy’s Magic Cast On’ is brilliant.
I had to redo it a few times before I understood, but then a light bulb clicked and I got it. It is like a toe up cast-on, however you do not close the loop to knit in rounds, rather turn around at one end and knit back and forth in stockinette.
I will knit this again for a different size for my soon to arrive grandson.

Update: grandson was born in August 2020 and he has been wearing the hoodie from 4 month to 8 month of age. Time to knit a larger size.