Nothing that I fly has or has ever had a return spring on the throttle, currently a 737 for work and a Piper cub for fun, the 737 is on a Certificate of Airworthiness and the cub on a Permit to fly. I have also flown home built aircraft with Volkswagen flat fours in and they do not have a return spring.
In any fixed wing aircraft you want the throttle to stay where you set it until you want to move it and to that end many have a friction control to lock it in place against movement from vibration.
An old colleague had a similar incident, having started the machine with chocks in place he taxied away with the fuel turned off and it stopped, he realised what was happening and turned the fuel on and pushed the throttle part way open, but didn't catch it. He jumped out leaving a non pilot passenger sitting in the machine and swung the propellor him self, the engine started and because he hadn't pulled the throttle back it started to move, he ducked under the strut and reached for the throttle and the door frame knocked him to the floor. He was fortunate that the lady passenger had her wits about her and turned the magnetos off and the engine stopped.
Inspection standards for Permit aircraft as in the news article are less stringent than for a commercial machine because they not be used for hire and reward, pre-flight checks are another thing entirely and if a pilot skimps those he would do so on any machine. It is correct that if the pilot had been in the machine and somebody swung it for him this wouldn't have happened, but finding someone both capable and willing to swing a prop can be difficult as most pilots train on aircraft with starter motors and have never been taught the art.
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