I am not the network guy at my office, but if you look at his code it uses special DNS records (look-up Zeroconf, it is a discovery protocol for services on a network). Do you remember using Apple iTunes back when you could share music with people on the same network? Same difference, so to speak.

If your VPN provider, you or otherwise, does not block the mDNS/Zeroconf network traffic and had a permissible DNS configuration (almost all commodity routers have mDNS/Zeroconf config available if not on by default), I am sure you will have this work. The author can answer you more clearly.