What they're talking about is cleaning a rifle from the muzzle.
When running a rod down the barrel from the muzzle, unless you use a muzzle guide to prevent the rod from contacting the delicate crown area, the rod can wear or damage it and reduce accuracy.
Since the AR can be cleaned from the chamber end, buy a good quality one-piece polished stainless steel or carbon fiber cleaning rod and a plastic chamber guide.
Clean the bore from the chamber end.
Allowing the rod to exit the muzzle by an inch or so will not damage it because you're not running a flexing, bending rod full length through the muzzle.
You can buy plastic chamber guides that lock into the receiver and these guide the rod into the bore and prevent getting dirty solvent in the receiver.
Another trick to reduce potential wear or damage to the bore is to PULL the rod.
Rods, especially .22 caliber rods are thin and they flex, rubbing the bore.
To prevent this, insert the rod through the chamber and out the muzzle.
Screw the brush or patch holder and patch on the rod, pull it back into the bore then apply a squirt of bore solvent and PULL the rod back out the chamber end.
This will not harm the muzzle and the rod won't flex or bend.