Just a thought.
I spent several years building my own aircraft, and although I am pretty competent with electronics, I am by no means an expert.
However I bought an off the shelf mode S transponder, set the hex code myself, installed it then test flew the aircraft. All done with no airframe or avionics experience, as is the case with a lot of home builders out there.
If you were able to smuggle a mode S transponder aboard that T7 I suspect it would be relatively easy for an electronically savvy guy to hook it up and set what ever hex code he desired thereby cloning another aircraft.
I am sure a licensed avionics engineer will shoot me down if I am way off the mark here.
But it may just explain why this guy appears to have been able to fly his aircraft wherever he wanted.