Not nearly deadly enough for protection...unless you empty the magazine into a perp.
No, it was probably a .223 or 5.56x45, the most common chambering for a AR15 clone.
The term AR15 clone is used because it covers the many different manufacturers and models that are made on the basic AR15 type of platform.
It has not been stated where Deishun L. Byrd-McWay was hit. There were likely peripheral hits, as he survived.