Your eyes do have to be open. Apple stated that.That does not make sense. It is not a retina scanner. But anyway, if he finds it an issue he can change the attentiveness settings: his eyes don’t even have to be open or looking at the screen to use Face ID.
my friend has contacts and without them in FaceID wont work. I asked him if they were colored and they are. So colored contacts are a no go. Makes sense though.