Yes Mr Beng thats what I worked it out as.
The cars are 1/32, only a couple of inches wide, and they are all plastic, 'cept for the dc motor.
However the radar modules are designed to detect people, and they are certainly not metal, in fact we are largely water which absorbs microwave energy to an extent, so I was thinking maybe these modules can 'see' plastic.
Fibreglass boats are fitted with a radar reflector if they want to be seen, having said that they work up to 40 miles on x band, we are talking about 20 meters.