Technically it is a 223 Wylde Chamber meaning it is a 223 cut with a bit different chamber leade to allow the use of higher pressure 556 in the "223" chamber.
Lots of AR's that are labeled 223 are Wylde cambered for this reason and they don't mention it prominently. The Wylde can shoot well but is generally regarded as not as cutting edge, accuracy wise, as a true 223.
I think if I saw an AR marked 223 that I would SUSPECT a Wylde chamber. If it were a bolt gun I would tend to go with the idea of a pure 223 non-Wylde chamber.
If it is a pure 556 AR than it really is a moot point as it will shoot 223 just fine for safety purposes and will, more than likely, shoot very well. It is almost a psychological issue at some point.
The bragging rights and needs of a "556" vs a "223" AR are very fine between some shooters. A High Power shooter is going to want a pure 223 match grade chamber. He wants it as close to ammo matching as he can get. I'm more of the on target results type of guy. I can make any of them shoot with some time at a reloading bench if the barrel is well done and things are not too out of spec.
The best firearm for self defense? Any loaded one will do.