“There’s a whole lot of ‘Do Not Travel’ areas out there (colored in red), including a few surprises.”
Yeah, but there is an important distinction between “Do Not Travel” and “May Not Travel.”
I think there is plenty of blame to share for this goat rope.
There is separate terminal for non-schengen flights at ZRH. Anybody flying from USA passes through passport control - whether they are connecting onwards or not. This is the same as in USA for anyone arriving from Europe (ICE/customs enforcment before connecting flight)
The ground staff at their point of departure seems to have dropped the ball in not checking their travel documents before they left for ZRH.