To pull a more articulate quote :
"For example, if Alice broadcasts the commitment with the most current state, Bob shouldn't be able to perform a penalty.
But if Alice broadcasts the revoked commitment transaction, Bob should be able to perform a penalty.
In order for Bob to perform a penalty:
* The transaction must have been revoked
* Bob needs to detect that Alice broadcast a revoked commitment transaction
* Bob needs to broadcast his penalty transaction that sweeps all of the funds before Alice is able to access her funds"