The degradation happens only when you explicitly start using a service (such as AirDrop) that uses AWDL. The AWDL interface becomes inactive once there is no more traffic on the interface. In the measurements, we show the performance when both infrastructure and AWDL traffic is present (i.e., the Wi-Fi radio needs to switch channels in between).

In fact one could argue that AWDL actually reduces "interference" because two neighboring devices can communicate directly and do not need to go an additional one-hop detour over an access point.