I've looked for articles and don't see anything about US weapons. It would be very strange, indeed, but supposition isn't proof and I can't find anything suggesting the US is involved in anyway. Colour me surprised, tbh.

I wasn't here to 'provide proof'. Just pointing out that any conflict beyond a certain size almost certainly has some weapon from every large arms producer deployed in the field. I can't image how many tons of small arms we left laying around in Iraq, Afghanistan and the rest that are now being recirculated around the worlds conflict zones. I remember after the Soviets pulled out of Afghanistan if you were in the right place and knew the right people you could get cases of NIB AKs for like $25 a rifle (no, I didn't). It's not politics...it's logistics.