PWM input specs of Hobbywing Quicrun WP-1040 ESC
Generally all RC gear uses the same old pulse-width modulation scheme: a pulse whose length varies between 1 and 2 ms, repeating every 20 ms. 

  

A pulse of 1 ms means "motor off"(airplane ESCs), "full reverse"(car ESCs) or "servo to the extreme left/right", while a pulse of 2 ms means "motor to full power" or "servo to the other extreme end".  

The 1 kHz specification in the manual is about the motor output. The ESC switches the H bridge MOSFETS at 1 kHz at varying duty cycles in order to precisely control the motor speed. 

A period of 20 ms means a frequency of 50 Hz, not 1 kHz like you assumed. Some components like RC helicopter tail rotor servos and multicopter ESCs are designed to also accept non-standard, higher frequency signals (500 Hz or less) for tighter control loops.