Seeing as he is a new moderator I feel like talking to him and correcting this situation would be the best thing to do here. The bank vault is indeed a restricted area and people can be arrested for being in the bank vault (The bank vault is referenced as a restricted area under the RDM rule "The player enters a highly restricted area such as the bank vault or back of PD." as well as it's a given that it's illegal to be inside the vault. I will see to the warning being removed and I will also speak to him regarding this situation and rule clarification. Thanks for the report.