Sure looks like a round that went into the chamber and deep seated due to insufficient case neck tension. Having worked for several manufacturers as an expert, and having blown up over a dozen ARs (on purpose), the damage is pretty typical for that failure mode. Less typical of a squib, but possible. That kind of failure really can only occur with ONE cartridge and bullet using pistol powder unless you deep seat a bullet with the ogive inside of the neck. Forged lowers typically fare just as well as billet and there is no evidence of anything wrong except ammo. Realize, if the owner insists on "fatigue" then he is done as far as pursuing the ammo manufacturer. Gots to be careful with videos...