In the crowd of over a thousand people, having two Level 3 New Humans was already tremendous. Provided they remained cautious, they could still survive in relative safety at this point during the apocalypse.
The reason they feared the car gang was that those outlaws were armed with guns. Even Level 3 New Humans, being human and not Level 3 zombies, couldn't withstand a bullet!
If luck weren't in favor, and a bullet hits a vital part, it would be a tragedy in waiting. Despite their numbers being in the thousands, they didn't possess a single gun, making a clash with the car gang potentially catastrophic.
Qiongli had also considered this issue, but she honestly didn't know if her conscience could bear leaving so many lives behind.
