Juan froze on the spot, he did not expect Anna to mention the security camera footage. He specifically chose that cafe to meet up with Rebecca because there is no security camera inside, but he did notice that there is one outside the cafe.
If the twins are going to check the footage, then Marcus will see who went in and out of the cafe. He and Rebecca came out of the cafe holding each other's hands. Marcus will see that scene and there is no chance for him to escape.
Juan looks at Anna's direction and saw she's bending her head down; in his view, it looks like Anna is about to cry, but Juan knows that she is only acting like in front of her grandfather.
Despite that, it is clear to him that Anna is driving him to a corner, but there is one thing that Juan couldn't understand. Why is it that Anna is not even nervous about what Marcus will see in the footage?