Sounds like they were logged into their Facebook accounts and he just followed the traffic to their pages and noted the info. He probably just used a network monitoring tool to do it. There are plenty of them out there. Some get pretty expensive tho...
Read the whole article. Bottom line. He uses a device which creates a network that people can log into and he can name it whatever he wants to so if you’re at a Starbucks and the network name is “Starbucks” but you see another network with a name like “Starbuckz” you better know which one is the correct one because if you log into the hacker’s network he can see all the data that our device is receiving and sending including your passwords. Clever little trick and simple but effective.