Both are correct. Reading further it STREAMS over a WiFi channel after linking via Bluetooth. So the AppleTV CAN'T be using a WiFi connection to a network at the time.

Found this blurb:
"Peer-to-Peer discovery is initiated using Bluetooth Low Energy (BTLE) when a user selects AirPlay on an iOS 8 or OS X Yosemite v/10.10 device. This causes the device and the Apple TV to visit Wi-Fi channel 149 in the 5 GHz band and Wi-Fi channel 6 in the 2.4 GHz band, where the discovery process continues. Once the user selects an Apple TV and AirPlay starts, the Wi-Fi radios timeshare between channel 149 and whichever infrastructure channel each device is currently using. If possible, the AirPlay sender roams to the same infrastructure channel the Apple TV is using. If neither device is currently using an infrastructure network, the devices will utilize Wi-Fi channel 149 only for AirPlay. Peer-to-peer mirroring adheres to 802.11 standards, sharing Wi-Fi bandwidth with other Wi-Fi devices."
[Link: chambersdaily.com]