IIRC the spawnargs for a func_pendulum are freq and speed, though "speed" effectively also acts as the swing angle (because the time period is already determined by freq).
Angles is just a generic spawnarg that describes how an entity is rotated on the horizontal plane.
Btw, the idea with binding a func_pendulum to a rotated model is to change the direction in which it swings. While the idea with binding a model to a func_pendulum, instead of making the model itself a func_pendulum, is to allow the model to swing from a different origin than its own.