The doctor who handled Dean must have said that he didn't call Rena at all. This certainly makes Rena think about his lie and what the lie was for Diego to do. Maybe by this time Rena had thought that Diego was a criminal who had bad intentions for her beloved grandson. With that in mind Diego can't stay here long. He couldn't possibly meet Rena. The middle-aged woman could have reported Diego to the authorities on charges of planned kidnapping.
Diego had to act fast and leave. Diego turned around and quickly knocked on the window several times, his eyes fixed on Elena. However, Elena, who was too late and focused only on Dean, was completely oblivious to Diego's code or signal. In panic, Diego looked back and saw Rena, who was getting closer. He couldn't stay here any longer.