Support for Bluesound Node 2i

I’ve been trying out Audirvana and really like it (especially for the SQ).
I usually run it on a Mac Mini with USB directly out to a Peachtree Nova 150 integrated amp.
However, this morning I selected my Bluesound Node 2i (streamer) as the audio output device (in the Mac menu), and its friendly name showed up in Audirvana’s output selection menu. Audirvana does send music to it, regardless of whether I’m using wired ethernet or WiFi. But the BS Node 2i supposedly does not support UPnP/DLNA. So how is this working? I thought Audirvana could only output via UPnP/DLNA over a network.