When Zhang Ziyang received Du Wei's message, he replied that he was informed.
After watching Du Wei's car driving away, Zhang Ziyang followed him.
Because Jiang Liluo just learned how to drive, he wasn't very skilled. Most importantly, he didn't have a driving license yet, so Zhang Ziyang was the driver.
Bodyguards didn't drive most of the time, since they were always by their hirers' side. They rarely did their job secretly, but it was very important for them to know how to drive.
For the time being, Jiang Liluo didn't have much time to learn how to drive, so it would take him longer to get a driving license.
If he went to do a task with his colleagues, his colleagues could drive. However, if he was going to carry out a task alone or with Si Jin, he needed to drive by himself.