Another case, with a lesson
A web search turned up another collision between a Piper and a helicopter back in April 1991 over Merion, Pennsylvania, when they got too close to each other (the helicopter was inspecting the landing gear of the Piper.) A rotor hit the fixed wing, and 6 people got killed, including Senator John Heinz.
What's of possibly helpful interest here is this analysis: A review of the literature on the aerodynamic interaction between fixed and rotary-wing aircraft in close proximity notes that there are two distinct and potentially hazardous aerodynamic concerns: (1) turbulence-induced blade stall and settling experienced by rotary-wing aircraft while flying in the turbulent area behind and below a fixed-wing aircraft, and (2) opposing pitch changes experienced by both aircraft when one flies close behind and below another.
The textbook Aerodynamics for Naval Aviators specifically refers to the case of one aircraft inspecting the landing gear of another. The lower aircraft may experience a nose-up pitching moment and the higher aircraft, a nose-down pitching moment. The author states that the opposing pitch-moment changes can be large and must be anticipated or a collision may result.
I wonder how many pilots today know about this hazard and whether it is included as part of their training.