seemingly brandishes a weapon which is - apparently - simultaneously belt and drum fed.
Doesn't look like that to me. Looks like it's drum fed on the blind side with a belt coiled in the drum. The visible belt appears to be spent (there being no bullets in it that I can see), so I guess it's of the type where a reloadable belt passes through "as is" (like a WW1 Maxim gun) rather then the bullets being linked with clips that detach, breaking up the belt, as it's fed.
I'm sure there'll be someone along in a minute to tell us exactly what that weapon is and how it works.