Is it possible he caught it in Shenzhen? Maybe only a few hours is all it takes.
It's not the fucking Zombie apocalypse. I'm still maintaining that you have a higher chance catching it in HK, there are certainly way less people out and about in Shenzhen. The whole city has a very "28 days later" feel to it and they have temperature checkpoints literally everywhere, every highway exit, every residential community entrance, every office building. Going from HK to our Shenzhen office will get you checked 3 times. Once at China customs when entering, once when leaving the highway, once when entering the industrial estate where our office is located. The highway toll exits are restricted to two lanes only, with police and staff in hazmat suits. On the way back it's once at the highway exit, once at China customs when leaving and once at HK border when arriving. They will check every passenger on all buses and have checkpoints before entering the MTR. Way more strict than in HK.