Ah you found my server! 
That’s interesting about the audio, the way it gets sent in the browser is in a specific way to try to avoid latency on retuning, but the system used does seem to have some quirks. I’ve found the same happens sometimes, but there’s ongoing development (the guy who came up with it only started developing it a few weeks ago, so it’s come along impressively fast already! - GitHub - NoobishSVK/fm-dx-webserver: FM-DX Webserver is a cross-platform web server designed for FM DXers who want to control their TEF668x/XDR receivers through a web interface. )
For the transmitter info, that comes from the RDS being decoded - it queries the database at https://maps.fmdx.pl and pulls through the transmitter by matching the PI code/PS and doing some logic based on power and distance if there’s more than one hit. If you click the PI code from the webserver it opens FMDX in a second tab with the transmitter and distance shown on a map.