The point is that if this were a fully automatic belt fed weapon, then quite a bit of planning must have been involved even just to acquire such a system, as opposed to a semi auto being bump fired from a magazine, which could be done at spur of the moment.
My guess is a full auto something with drum magazines.
Shots sounded too rhythmic to me to have been a semi/bump arrangement.
Breaks in firing due to changing weapons and/or mags.
I’m certainly no expert, but you’re correct in thinking we have a motherlode of guys/gals in here who are !
That co-ping above oughta get you some authoritative answers.