The line is a guide at the EXACT measurement of where you need to fill to. It's a lot easier and more accurate to fill to the meniscus specifically to that line than it is to fill a 10ml syringe and push it out with the air bubbles and what not. A 10ml syringe will get your meniscus to that line perfectly regardless.
The only other thing that could cause crazy high readings like a .67 are finger prints, and micro-bubbles. Not shaking the cuvette enough will show lower readings as will not mixing for a total of 2 minutes on the dot.
If his meniscus is not perfectly on the line then he needs to get it there and re-test.
If the plunger of the syring is bottomed out when you draw in solution, it makes no difference if there is a bubble in it or not, 10ml of water will still come out of it. Anyone that believes they can eyeball that line better than a syringe is crazy.