Little Snitch reports outgoing connections for AirPlayXPCHelper for wrong subnets?
Time to answer my own question:


  Why AirPlayXPCHelper goes out to this network on port 5000 and 7000?


This is related to the Peer-to-Peer AirPlay and Airplay device discovery. macOS discovers new device and attempts to connect using these ports to finish (?) discovery process. 

Couple of my neighbours got new AppleTV and macOS attempts to connect to them. As all AppleTVs are connected to the different networks, it attempts to connect to each of them and it is what Little Snitch reports.


  Is there a way to limit its desire to go there?


I'm not aware of any. I just blocked access for AirPlayXPCHelper to networks other than mine using Little Snitch.