CNN reached the pilot of the helicopter Williams was on. Pilot was quite gracious and wound up confirming much of William's version, some details were off.
* Multiple choppers, lead one was fired on with RPG
* William chopper (#2) was fired on and hit by small arms fire. Door gunners returned fire
* Lead chopper set down immediately
* Chopper 2 & 3 continued on mission to drop their load (bridge parts) and returned to chopper #1 where it landed (so yes, some small delay)
* Chinook crews were the ones that set up the perimeter; ground units happened by much later (day +)
So Williams's story would seem to be more true than not. The group of helicopters he was with took RPG fire (his particular one was 6 rotor blades away says the pilot). His particular chopper did receive small arms fire. They did all wind up landing together and there was a perimeter set up, but the ground troops came later.