In that light, it's odd that they specify a polling rate at all, since they use direct-attached key pins linked to an 48MHz clock. There is no grid/matrix sensing period, which is usually what is meant by polling rate. And the claimed value of 1kHz is doubly weird since the debouncing logic uses a period of 5ms, which means they can at most mimic a 200Hz polling rate:

  entity Debouncer is
    generic (
      FILTER_DURATION: delay_length := 5 ms
    );

edit: looked up what the typical bounce time is for a keyboard switch, and 5ms seems to be pretty standard. It's also the default that QMK uses. It seems quite excessive to me, I'd have expected bouncing times to be closer to tens of microseconds than multiple milliseconds.