“We had no such law that required us to protect customers from other customers.”
The protesters creating the disturbance at the restaurant were not “customers”. They were invaders who were intentionally disturbing the dining experience for Cruz and the other real paying customers.
A small business owner who does not take action when her/his place of business is invaded by agitators intent on destroying the ability of paying customers to purchases goods/services and use/consume the product purchased will soon find there are no customers.
He did take action. He got rid of the protesters after taking the Cruzes to safety. What more do you want of the owner?