Yes, the guardian app allows you to send encrypted messages through their app to their journalists. 100,000 people check the news, one person is whistleblowing. That one person’s messaging traffic is mixed in with the regular news data, so it’s not possible to tell which of those 100,000 people are the source. Signal messages travel through their servers, so anyone inspecting packets can see who is sending messages through signal, just not what the messages contain. Thats a big red arrow pointing to only people sending encrypted messages. With this implementation, those people are mixed in with everyone else just reading news or even just having the app on their device.