There are times when localbitcoins keeps updating the list of excluded third parties and the "third party" you are using has just been added. Anyway in essence you violated their terms of use long ago:
Receiving, making, providing, or attempting to receive, make or provide payments to or from third parties is forbidden and considered a violation of this Agreement unless authorised by the third party.
Or account locking may be done manually, so your penalty is executed recently.