Maybe the restaurant was posted and the good guys had stored their firearms in the trunk while they were eating.
TITLE 21 § 1290.22 - BUSINESS OWNER’S RIGHTS
A. Except as provided in subsection B of this section, nothing contained in any provision of the Oklahoma Self-Defense Act, … shall be construed to limit, restrict or prohibit in any manner the existing rights of any person, property owner, tenant, employer, or business entity to control the possession of weapons on any property owned or controlled by the person or business entity.
B. No person, property owner, tenant, employer, or business entity shall be permitted to establish any policy or rule that has the effect of prohibiting any person, except a convicted felon, from transporting and storing firearms in a locked vehicle on any property set aside for any vehicle.