What I'd ask people to consider is that these reports started coming in around 1946 - 48, i.e. at the precise time that many people riding around in piston engined aircraft started seeing the occasional jet go by them at two to three times their own rate of speed. A P51 or F8 might have had an outright top speed of 430 or thereabouts, but no piston engined plane ever cruised at that speed; cruising speed for piston engined planes was never much more than 250.