I suspect maybe he is loosening the head rather than the nozzle, and the nozzle has been deformed into a slight trumpet shape. The Neo nozzle is very fragile. The space between the nozzle and head for air to exit from the Neo is very small. If the nozzle is deformed, it will choke off the air enough so that there isn't enough to draw paint. Loosening the head increases this gap, but too much will cause blowback into the cup. A fresh nozzle might fix his problem.
Another possibility is that the rubber o-ring is pinched between the nozzle and body of the airbrush. See my review for a photo.
Don