The study your referring to is the Minnesota starvation study.
It placed individuals on a severe caloric deficit(IIRC 40%+) with low protein intake, no resistance training and low intensity cardio (walking, farm work, etc) as the only notable activity for just over a year.
All the individuals hit 5%bf without fail.
The study showed that muscle loss will NEVER overtake fat loss but certainly didn't suggest that you can get away with low protein intake.
Of the total weight lost, 40% came from LBM - that is ALOT.
Most people tend to lose around 1 pound of LBM for every 4 pounds of fat loss (25%) with good protein intake & training in place. Of course this depends on p-ratio, etc but is a good guideline to show what is acceptable.
In short, cutting on a low protein diet is a pretty fucking stupid idea since higher protein intake is the best saviour of your own protein stores AKA your muscles