Does anyone know what weapon Lil Baby is using?

Not sure if this is the right sub for this question. It looks like Lil Baby, in blue, is using a short barrel AR platform with the stock removed. If that is the weapon does anyone know why that would be chosen over an SMG or PDW.

P.s. As a non-american gun enthusiast I'm often confused by American firearms but I'm assuming this weapon choice is about practically rather than gun law restrictions