No, this has nothing to do with the posture of our necks! We are looking at the positions of the left hand on the neck of the cello!
I have sometimes used the "upper" and "lower" terms with 2nd and 3rd positions as per Rick Mooney's book, Position Pieces, but most of the time the somewhat moveable 2nd and 3rd position indications are a little more vague. I like the way Robert Jesselson explains things here, using the terms "2nd and a half" and "3rd and a half", etc., and the chart he shows. Take a look!
Students: Is there a "4th and a half" position? Please be ready to show me on your cello at your next lesson!
Geography #1 – Position chart and VII position harmonic