One-handed Swing Technique

I was watching the ETK video and have a question regarding the one-handed swing technique. In some one-handed moves (e.g. the set up for the clean) Pavel hike passes the bell with his thumb facing backward.

On the downward (hike pass) motion of the standard one-handed swing are we supposed to rotate the thumb backward as the bell moves to the bottom or are we supposed to keep the palm facing backward the the bell oriented in the same position for the entire swing? Are both acceptable?

Any insight is greatly appreciated.