It was some filter on their router. The casting here only seems to be in apps. I have to pull up Chrome in order to cast.
My a friend is using a Nexus 5X to pair with a Chromecast on a flatscreen, but today she noticed that the Chromecast no longer showed up in the "Cast" menu. The only options listed now when it's pressed in any app will be "This device" and "nearby device" options. When the "nearby device" option is selected, the phone wants to use the microphone to listen for a nearby device. Obviously not right. I can still connect to her Chromecast on my phone just fine. What could be going wrong on her phone?