The qualifier of propellor-driven-ness aside, gun kills were very much a thing through the Vietnam War, and there are recorded gun kills from modern aircraft in the 90s (an A-10 downed an Iraqi Mi-8 with its 30mm in 1991, and Venezuelan F-16s are recorded knocking down prop-driven recon and close air support aircraft with their 20mm cannons in 1992. It's only been relatively recently that missiles and IFF systems have become reliable enough to obviate the need for dogfighting capabilities and weapon systems.

If anything, standout thing here is the kills being achieved by a backseater with an assault rifle of some variety. "Lean out of the cockpit and shoot your service weapon at the other guy" aerial combat hasn't been in vogue since the earliest days of World War 1, but given the low speed and predictable flight profiles of the drones these guys are targeting, it's not a bad choice.