Yes this is because I’m assuming your raspberry pi doesn’t have an internet addressable domain name. And the widgets on the radio page rely upon the URL to load. So it might be pointing to say localhost - which works for the raspberry pi but any other computer will think it’s pointing to itself. It could also just be using whatever domain name raspberry pi used as the host.
There are a few ways of fixing it but I don’t think they have been super well documented. It is probably easy to do w/o SSL via setting up a CORLS forwarder, and you can use SSL and lets encrypt with a proxy - this issue shows that people have done it but are also still running into issues, so we need someone to take this issue on and write the documentation for how to resolve it and/or submit any code fixes.