Part 107 pilot reported observing another UAS operator flying a nearby UAS have a near miss with a general aviation aircraft on climb out.

Narrative

While occupied with another task; I noticed another UAS operation in my vicinity. We were located very close to a busy Class B airport and were accustomed to hearing departing air traffic. Departing traffic was headed either southbound or westbound for much of the day; but recently shifted to northbound departures. This runway change moved departure traffic's crosswind turn to within a mile of our site.Departing airline traffic was no factor - their predictable routing and higher climb gradient meant they were well outside of possible collision hazards. Piston airplanes; however; required situational awareness and foresight to retain appropriate separation. I was not flying my aircraft at this time; but I looked around quickly upon hearing a piston-powered airplane. The early afternoon sun made it hard to see oncoming traffic from the east. I gained visual sight of a Cessna departing on an early crosswind turnout to the west from Runway XX. The other operator was not from my organization; nor were we operating together. But due to the urgency; I alerted the RPIC who immediately began a descent. The Cessna passed directly over and; likely; within 100 ft. of altitude from the other operator's UAS. Local environment was one causal factor: high buildings and obstructions blocked much of the VO's view. Poor situational awareness on behalf of both the other operator and his VO led to late detection of manned air traffic. The VO was likely in a poor position to execute his task of scanning for traffic. No radios or internet-supplied traffic data appeared to be in use by the operator. This operator had no knowledge of visual separation minimums. When asked about mitigating altitude conflict with the local traffic; the RPIC referenced his airspace authorization. He overlooked the fact that a UAS airspace authorization does not free the RPIC from see-and-avoid responsibilities. To his credit though; he did make a timely evasive action once the imminent threat was detected. This operator and his operation lacked the professionalism and situational awareness necessary to fly in a complex airspace near Class B airport operations. More awareness for UAS operators on manned flight procedures would have aided this party in reducing the risk posed to manned aviation. Jet traffic likely led to complacency for this operator; who then had no knowledge of instrument Departure Procedures or airplane performance to aid in his risk management.