Allmost all compressor motors, I believe, are rewind on 1 pair of poles. That is, at 50Hz they rotate 3000 rpm minus "slip", or "lag", or "friction" (difference between rotating field in the stator and the actual rotations per minute).
60 Hz motors rotate 3600 rpm - the slip.

The only explanation I can come with for an (asynchronous) motor able to work both 380 -420V 50HZ and 460V 60Hz is its universality.

But universality does not mean that at the same load but different voltages and frequencies it will have the same speed, draw the same current, be able to produce the same work. It is rather something averaged around the numbers which the manufacturers specify.

To put it short, at 380V 50Hz the motor is slowest and lest powerful. At 460V 60Hz the same motor is quickest and most powerful.