This is by design and unavoidable. To ensure that Quantiloop reacts immediately to start commands, it will start playing as soon as you depress the pedal/button. As soon as the hold triggers the loop will be deleted.
An alternative way to delete a loop however is:
Double Tap and then Hold the Loop Button
This action can even be performed while a loop is playing. As the double tap is very fast no sound should be audible on this action.